Introduction

Shipwrecks are unique archaeological sites, akin to time capsules that contain a comprehensive snapshot of a particular era (Song 2018). They serve as repositories, not only of the cargo aboard the ship, but also as nuanced temporal and spatial information, such as the background of the era, maritime routes, and sociopolitical dynamics. They also offer insights into the political and social ecologies of the time. The tangible artifacts unearthed through maritime archaeology serve as direct evidence of material exchange between regions and provide valuable insights into maritime economic activities. These findings shed light on specific historical periods of a nation or region, capturing fragments of civilization from bygone eras. By carefully examining these artifacts and integrating them with the historical record, scholars can uncover a variety of historical truths (Huang and Feng 2021).

During the period of the Northern and Southern Song Dynasties in China (960–1279 ADFootnote 1), while there exists an abundance of historical records documenting overseas trade activities, direct material evidence has been lacking. Since the 1970s, with the unveiling of archaeological discoveries such as the Southern Song shipwrecks of Houzhu (Quanzhou Maritime Museum 2017, 227–234), Nanhai No.1 (GPICRA 2011; Sun et al. 2016; Wang and Xiao 2016; NCUCH et al. 2017a, b; Sun 2020), and Huaguangjiao No.1 (Meng 2018), Chinese scholars have made significant advancements in the study of overseas trade during the Song Dynasty with the discovery of tangible artifacts. Among the numerous archaeological findings, the Nanhai No.1 shipwreck is one of the most remarkable archaeological finds due to its well-preserved state, the abundance of artifacts recovered, and its direct evidential value.

Nanhai No.1 stands as possibly the best representative of Song Dynasty maritime trade in the South China Sea region, offering valuable material evidence for the study of ancient Chinese trade history, shipbuilding history, ceramic history, and overseas transportation history. What sets this vessel apart is that it sank shortly after setting sail and before venturing far from the Chinese coast into deeper waters, making it a rare example of an ocean-going merchant vessel (Sun 2020). The cargo it carried can provide insights into the composition of Chinese trade goods at the time. Moreover, Nanhai No.1 was salvaged integrally as a whole and comprehensively excavated on land (NCUCH et al. 2017b), resulting in an unparalleled completeness and richness of both the ship's hull and its onboard artifacts compared to other ancient shipwrecks discovered to date.

The excavation of Nanhai No.1 concluded in 2023, yielding around 180,000 individual pieces or sets of various artifacts (as of the data available until 2019). The artifacts included numerous metal relics, such as gold, silver, copper, and iron. The iron alone weighed about 124 tons, and the silver exceeded 300 kg (NCUCH et al. 2017b, 419–518; Li 2021). It is noteworthy that the metal cargo was not exclusive to Nanhai No.1; other shipwrecks from the same period in the South China Sea region, such as Huaguangjiao No.1 (Meng 2018) and Java Sea (Flecker 2003; Mathers and Flecker 1997), also yielded abundant metal artifacts, indicating the significance of these metal goods as essential commodities of the time. One aspect that has usually been overlooked in previous studies is that, throughout the Song Dynasty, various metal raw materials and products were strictly prohibited from export by the Song government (Huang 2019). This apparent contradiction is at odds with the substantial metal cargo unearthed through archaeological findings. The discovery of Nanhai No.1 provides an opportunity to explore the patterns of metal trade in the South China Sea region during the Song Dynasty.

Nanhai No.1 Shipwreck

The Archaeological Discovery of Nanhai No.1

Nanhai No.1 is a Chinese merchant ship from the Southern Song Dynasty (1127–1279 AD) that foundered while fully laden with cargo. It sailed from the southern port of Guangzhou in China and sank in the waters near the junction of Taishan and Yangjiang cities in Guangdong Province, at a depth of approximately 24–26 m (Fig. 1), en route to conducting trade activities in Southeast Asia and West Asia. Discovered in 1987, the shipwreck was salvaged in 2007 and transferred to the Guangdong Maritime Silk Road Museum for conservation (GPICRA 2011). In late 2013, comprehensive conservation and excavation work commenced on Nanhai No.1 (Sun 2020), with the excavation of the cargo completed in 2019 and the entire excavation project concluded in 2023.Footnote 2 The shipwreck is relatively well-preserved and has some three-dimensional structure. The remaining hull measures approximately 22 m in length, with a maximum width of approximately 9.8 m and a hold depth of 2.7 m. The hull is divided into 15 compartments by watertight bulkheads (Fig. 2). The ship also had superstructures, although the surviving hull remnants lack the upper structure at the stern, rendering the architectural layout unclear (NCUCH et al. 2017b, 110–115, 127).

Fig. 1
figure 1

Location of places and shipwrecks mentioned in the text. Places: 1. Bianjing (Kaifeng); 2. Lin'an (Hangzhou); 3. Ningbo; 4. Jingdezhen; 5. Quanzhou; 6. Guangzhou; 7. Khao Chai Son; 8. Kota Cina. Shipwrecks: a Nanhai No.1; b Huaguangjiao No.1; c Quanzhou Bay; d Java Sea; e. Intan; f Cirebon. The red line represents the approximate sailing route of Nanhai No.1 before its maritime disaster

Full size image
Fig. 2
figure 2

Orthophoto image of the excavation process of Nanhai No.1 on land. The yellow lines indicate bulkheads and C1-C15 represent compartments 1–15

Full size image

Nanhai No.1 yielded a diverse array of artifacts, encompassing ceramics, metalware (i.e. gold, silver, copper, iron, lead, zinc, and tin), lacquerware, wooden items, coins, cinnabar, animal remains, and plant remains (Sun et al. 2016; NCUCH et al. 2017a, b). According to historical documentation detailing Song Dynasty foreign trade commodities, silk was also prominently featured among the cargo (Zhao 1996, 34–43, 55). Despite extensive degradation of organic materials due to prolonged immersion in seawater, residue analysis of soil samples extracted from various cargo holds provided evidence of silk protein, affirming the presence of silk textiles among the cargo (Li et al. 2019; Sun 2020). As of 2019, the excavation has unearthed nearly 180,000 artifacts, comprising approximately 160,000 pieces of ceramics and 124 tons of iron concretions. Noteworthy among the recovered items are a substantial quantity of metal currency, including copper coins, gold leaves, and silver ingots, many of which bear inscriptions in Chinese characters indicating shop names, weights, and addresses (Li 2020b, d, 2021). Furthermore, the excavation yielded a variety of gold jewelry items, including rings, bracelets, belt accessories, and necklaces, adding to the richness of the discovery (Li 2020c).

The distribution and loading patterns of various cargo types within the compartments of the ship exhibit discernible regularities. From the bow to the stern, the main cargo within each compartment consists of neatly stacked ceramics. Substantial amounts of metal semi-finished products, such as iron bars, ingots, and pots, are also present and are arranged vertically above the ceramics. These items are widely distributed horizontally across multiple compartments, forming large concretions during the seabed burial process (Tian 2020; Fig. 3). Specifically, semi-finished iron pieces are primarily loaded in compartments 2, 3, 4, 5, 7, and 11, with a small quantity of iron pots in compartment 5, and compartments 6 and 12 containing both iron pots and semi-finished pieces. Compartments 6 and 7, located near the main mast, exhibit the densest concentration of ironware, possibly for the sake of ship stability (NCUCH et al. 2017b, 496). Silverware is predominantly recovered from layers of seabed sediment in compartments 3 and 4 (NCUCH et al. 2017b, 432; Fig. 3). Inside the compartments were found copper coins, and over 108 complete or nearly complete copper rings and dozens of ring fragments that were originally placed inside ceramic cosmetic boxes. However, due to the agitation and vibration during the integral salvage operation, most of the copper rings spilled out of the cosmetic boxes (NCUCH et al. 2017b, 487). Other metal findings include over 20 kg of tinware and tin beads, four zinc fish-shaped pendants, and several lead net weights ranging in weight from 11 to 47 g (Fig. 3).

Fig. 3
figure 3

a, b Iron bars; c A silver ingot concretion; d A silver ingot with Chinese inscriptions; e Copper rings hidden inside in a cosmetic box; f A gold leaf with Chinese inscriptions; g Tin beads; h A zinc fish-shaped pendant

Full size image

Based on the ink inscriptions found on the undersides of ceramics and the era names on copper coins, as well as radiocarbon dating results, the current assessment suggests that Nanhai No.1 likely foundered in 1183 AD or shortly thereafter (Li 2020c). Assessing the origins and distribution centers of the cargo onboard provides insight into the likely route of Nanhai No.1, which traversed from Zhejiang to Fujian and then to Guangdong provinces (Li 2021; Fig. 1). The ship made significant stops in Zhejiang Province, including Hangzhou (called as Lin’an in the Southern Song Dynasty) and Ningbo cities, where substantial procurement and loading activities transpired, including the acquisition of Jingdezhen porcelain, gold leaves, and silver ingots. It then made a stop in Fujian Province, such as Quanzhou City, to load porcelain, before finally stopping in Guangdong Province, specifically Guangzhou City, to load ceramics and alcoholic beverages before starting its voyage to Southeast Asia.

The Value of the Cargo

During the Song Dynasty, the common cargo on outbound maritime trade ships included ceramics, ironware, gold, silver, alcohol, silk, spices, and medicinal herbs, among others (Chen and Wu 1984, 46, 54–57; Qi 1988, 1046–1048). However, due to the large quantity and preservation of ceramics, they have often been the focus of previous research, leading to the misconception that ceramics were the primary commodity of value aboard these vessels. While it is true that ceramics make up the vast majority in terms of quantity among the artifacts recovered from Nanhai No.1, a reassessment based on estimated monetary values reveals that they were far less valuable in terms of commodity value compared to the iron and silver on board (Li 2021; Table 1). This finding differs significantly from the previous perception that ceramics were the most important cargo. The prices of gold, silver, and iron are estimated based on historical records from the Southern Song Dynasty. Similarly, the prices of ceramic are derived from ink inscriptions found on the bottoms of Song Dynasty ceramic pieces. Due to variations in form and quality, the price of individual pieces of ceramic ranged from 6 to 70 copper coins. For estimation purposes, a median value of 35 coins was used in the study. Although the prices of different commodities fluctuated over different periods and regions, Li’s (2021) study provides valuable insights into understanding the relative value of different types of cargo.

Table 1 Valuation of ceramic and major metal commodities. All unit price and totals in the table are measured in copper coins. The prices of gold, silver and iron reflect the cost of raw materials during the Southern Song Dynasty, with the prices of finished products (such as iron pots, gold leaves, gold jewellery and silver ingots) being higher. The estimated cost of ship construction is 10,000,000 copper coins (information adapted from Li 2021)
Full size table

Although valuable commodities such as silk have not been preserved, analysis of silk protein residues suggests that silk was likely among the cargo of Nanhai No.1 (Sun 2020), albeit its value cannot be quantified. Moreover, the significant presence of metal artifacts on Nanhai No.1 is not an isolated case. Similar findings of metal artifacts, predominantly ironware, have been made on other shipwrecks such as Huaguangjiao No.1 (Meng 2018) and Java Sea (Mathers and Flecker 1997, 77–95; Flecker 2003). In assessing the value of the cargo, these metal artifacts are comparable to, and probably exceed, the importance of the ceramics.

Li (2021) estimated the value of metal goods based on their trade value within China, but the actual prices of metal artifacts when exported were probably higher. Due to the strict prohibition on metal trade imposed by the Song government, ship owners caught smuggling metal artifacts abroad would face severe penalties (Li 2004, 11435–11462; Xu 2014: Penal Law ii 8340, 8387). The fact that ship owners were willing to take such significant risks to transport prohibited items (e.g. gold, silver, copper and iron) suggests substantial profit potential, indicating that the prices upon arrival at the destination port were likely much higher than the prices at departure. Smuggling prohibited goods was highly lucrative; for example, smuggling copper coins abroad often yielded profits at least ten times the initial investment, as documented in Chinese literature during Song Dynasty (Bao 2006). In contrast, while the prices of ceramics may have increased upon export as well, they would unlikely command the same tenfold premium as metal contraband. As a result, the prices of metal artifacts shipped from China to Southeast Asia in previous studies may have been significantly underestimated.

Trade Administration in the Song Dynasty

Shibosi (Maritime Trade Bureau)

During the prosperous maritime trade of the Song Dynasty, in order to effectively manage overseas trading activities, the Northern Song Dynasty established the Guangnan Shibosi located in Guangzhou at its inception, marking the beginning of the establishment of market agency institutions during the Song Dynasty (Yang 2004, 4). The Songshi (the History of the Song, an official Chinese historical text) documents: "Shibosi is responsible for the trade and taxation of foreign goods and maritime trade, dealing with people and their goods from distant lands” (Tuotuo et al. 1985: S167 Treatise on state offices vii 3971). Throughout the Northern and Southern Song periods, as maritime trade conditions evolved, the Song government continually adjusted the distribution of market agency institutions in coastal ports. However, the Shibosi in Guangzhou, the earliest to be established, consistently maintained a significant position (Yang 2004, 5–8).

The Shibosi, responsible for both trade and diplomatic functions, regulated all types of trading merchant ships coming to and from China (Tuotuo et al. 1985: chapter 167 Treatise on state offices vii 3971; Xu 2014: chapter State Offices xliv 3369). Under the laws of the time, merchant ships were required to follow prescribed procedures when arriving in and departing from Chinese ports (Fig. 4) or face penalties for smuggling. Taking the example of Chinese merchant ships departing from China, maritime traders were required to submit a permit (Gongping) application to the Shibosi (Su 1986, 889–890), detailing information such as the names of crew members, the names of goods and the destination. Only after obtaining the Gongping could the merchant ship legally engage in maritime trade (Huang and Feng 2021). Before departure, representatives from the Shibosi and the local government at the port jointly inspected the ship, verifying passengers, cargo, and ensuring compliance with smuggling regulations. After inspection, the ship was escorted by supervising officers to navigate into deep-sea routes (Xu 2014: chapter State Offices xliv 4215). Upon returning to China, merchants had to surrender their Gongping to the Shibosi, who then inspected the permits and goods, collected taxes (Choujie), and exercised the government's right of first refusal (Bomai). The Shibosi issued certificates for Choujie and Bomai, along with a list of goods (Yinmu), allowing merchants to legally sell the repatriated merchandise within China (Xu 2014: chapter State Offices xliv 4207). Failure to comply with these legal procedures rendered the cargo liable for seizure as contraband. Owners of ships carrying such goods would face severe punishment from the authorities, including confiscation of all goods: "Anyone who dares to smuggle goods without Choujie will forfeit all goods” (Xu 2014: chapter State Offices xliv 4207). Foreign merchant ships arriving in China were also subject to regulation by the Shibosi.

Fig. 4
figure 4

A flowchart depicting the process of a legitimate merchant ship from departure to return to China

Full size image

Trade Embargo

It is important to note that the management scope of the aforementioned Shibosi system is limited to legally traded goods, as some goods are prohibited items explicitly banned from export trade by the Song government. Due to hostile relations with the Liao and Jin regimes in the north, the Song government banned the export of military equipment and related materials such as copper, iron, arrow shafts, and cowhide. Additionally, precious metals and currency such as gold, silver, and copper coins were also prohibited from export (Quan 1972, 501–504). Merchants who violated these prohibitions would face confiscation of their cargo and imprisonment (Li 2004, 11435–11462; Xu 2014: chapter Penal Law ii 8340, 8387), and the government also set up a system to reward informants (Guo 2008). Apart from the trade embargoes on specific goods, the Song government also enforced strict trade embargoes on certain regions. For instance, the Northern Song prohibited merchants from engaging in trade within the territory of the Liao and in areas proximate to the Liao. Similarly, the Southern Song forbade merchants from engaging in trade with the Jin via sea routes. Both Northern and Southern Song consistently prohibited their own merchants from trading with Annam (corresponds to present-day northern Vietnam), and at one point, also banned trade with Goryeo (the Korean Peninsula) (Huang and Feng 2021).

Tribute Trade

In ancient China, there existed a unique form of interaction known as the tribute trade, through which certain prohibited items stipulated by the Song government could be legally imported and exported from within the borders of the Song Dynasty. Tribute trade refers to the practice wherein countries outside of China, ethnic minority regimes, or local separatist regimes paid homage to the centralized Chinese dynasties or influential regional powers by acknowledging vassalage and offering tribute, in return for investiture and rewards. This practice had strong official and commercial connotations (Chen 2014, 1). On the surface, it was a political-diplomatic relationship, but in reality, it was also a form of trade relationship, albeit one in which the political significance of the tribute trade far outweighed its economic implications.

The Song government allowed foreign envoys to trade with China on condition that they paid tribute. Representatives from various countries were required to attend a series of elaborate tribute ceremonies upon arrival in the capital, Bianjing (capital of the Northern Song) or Lin'an (capital of the Southern Song). These ceremonies included the presentation of their country's official seals and tributes, audiences with the emperor, participation in ceremonial rituals and banquets, and the receipt of various rewards from the Chinese authorities, often exceeding the value of the tributes offered (Zhang 1998). The tributes typically consisted of goods produced within their own countries, as well as certain animals, such as ivory, rhinoceros’ horns, aromatic woods, incense, tortoise shells, pearls, and precious metals, along with exotic animals such as elephants and lions. The reciprocal gifts from the Song Dynasty were also highly prized and included copper coins, gold and silverware, clothing, bedding, footwear, silk fabrics, horses, and certain animals. Sometimes, at the request of tributary states, the Song Dynasty would also offer books, weapons, armor and other items (Zhang 1998; Huang 2011, 117–124). It is noteworthy that among these tribute and reciprocal gifts often included items that were prohibited by the Song Dynasty regulations. Items that were prohibited in maritime trade were purchased in full by the Chinese government; for items that were not prohibited, the remainder was allowed for private trade, in addition to the portion allocated for court and government purchases. The portion purchased by the court and government was consumed within the palace or given as rewards, and the remainder could be resold (He et al. 1990, 2006). In essence, prohibited items such as gold, silver, copper coins, and even weapons could be legally imported and exported from within the borders of the Song Dynasty through the tribute trade.

Metal Trade in the South China Sea

In ancient international trade, metal raw materials or metal products were crucial commodities, used for crafting weapons or agricultural tools. Additionally, metals were valuable ballast materials aboard merchant ships (Li 2012). From the 10th to the thirteenth century, China played a significant role in the metal trade within the South China Sea region. China made notable advancements in metal smelting and processing technologies and, leveraging economies of scale, its metal raw materials and products surpassed those of manufacturers in Southeast and South Asia in terms of competitiveness. Before the arrival of European competitors, China had a virtual monopoly as the main exporter of metal goods to the South China Sea region (Flecker 2002, 86–87).

Due to the varying quality or corrosion resistance of goods, many cargoes carried by sunken ships have disappeared over time as a result of prolonged immersion in seawater. The ships themselves often corrode and deteriorate, vanishing without a trace. However, solid blocks of copper, iron, lead, tin, as well as gold and silver, frequently appear among the relics of ancient shipwrecks in the South China Sea region from the 10th to the thirteenth centuries. For example, the Intan shipwreck yielded tin ingots, lead ingots, various iron objects, along with 500 pieces of gold foil and gold and silver jewellry (Liebner 2014, 183–184). The Java Sea shipwreck revealed a variety of metal raw materials and artifacts, including 865 kg of copper ingots, 792 kg of tin ingots, 479 kg of copper alloys, 596 door handles, and 652 bronze mirrors (Flecker 2002, 29–30), as well as approximately 190 tons of ironware, possibly originating from China (Mathers and Flecker 1997, 101–102; Flecker 2003, 388–404). Furthermore, the metal items discovered did not solely originate from China; there were also metals from Southeast Asia, such as copper mirrors from Indonesia (Flecker 2002, 29) and tin ingots from the Malay Peninsula (Flecker 2002, 82–83). Nonetheless, Chinese metal artifacts held a predominant position among the metal items uncovered.

The continuous high demand for hard currency in maritime trade within the South China Sea region naturally led to the circulation of currencies from relevant trading nations in the international market, serving as a general equivalent and medium of exchange. As a result, many countries around the South China Sea adopted the practice of using foreign currencies, with Chinese copper coins being frequently discovered in archaeological sites across Southeast Asia (Li 2012). Among Chinese currencies, Song Dynasty coins were the most prevalent, owing to the flourishing overseas trade and developed monetary economy of the time, as well as the exquisite craftsmanship of Song coins (Peng 2007, 296–298, 333). Archaeological findings reveal that countries and regions engaged in trade with China, including South Asia and West Asia, have discovered Chinese coins (Yao 1998, 147–154). It is worth noting that not all Chinese copper coins that entered Southeast Asia were used as currency. Some were considered valuable metal materials and melted down to produce various household items such as pots, pans, plates, bowls, or ornaments. Until the fourteenth century, Indian, Persian, Acehnese, Siamese, and Arab merchants, as well as local traders in Malacca, bought significant amounts of Chinese copper coins to melt and craft various kitchen utensils or decorative items (Nge 2005, 140).

Gold, silver, and other precious metals have also been frequently discovered in the South China Sea region. Apart from serving as a medium of currency exchange (Li 2020b, d; Ding 2022), they were also crafted into exquisite jewellry and ornaments and traded to Southeast Asia, West Asia, and other regions (Li 2020c). On Nanhai No.1, suspected commercial items such as gold earrings, rings and necklaces were found, with the rings displaying distinct West Asian styles and featuring settings reserved for gemstones. Researchers believe these were semi-finished products made to meet the requirements of West Asian buyers. They were transported to the region for gemstone setting, indicating the existence of a gold and silver trade and processing industry along the Maritime Silk Road during the Song Dynasty, covering trade routes from China to West Asia (Li 2020c). The unearthing of Chinese copper weight in the ancient port of Al Serrian, Saudi Arabia (Li 2020c), indicates strong trade ties between the eastern and western regions of Asia in the trade of precious metals.

Discussion

During the Song Dynasty, metal goods had consistently been one of the primary commodities in the South China Sea region. However, there has been little scholarly exploration into the fact that these metal commodities, which were exported from China, a significant metal exporter, were classified as contraband and expressly prohibited for export during the Song Dynasty. One of the main reasons for this phenomenon can be attributed to the scarcity of relevant archaeological data in the past. The salvage excavation of shipwrecks in the South China Sea region has provided scholars with new material. This has created an opportunity to link commonly traded commodities with prohibited goods in Song Dynasty trade. This prompts an inquiry into why metal goods were classified as contraband while concurrently enjoying popularity in the markets of the South China Sea region.

Legal or Not

Metal artifacts recovered from Nanhai No.1 include tin, lead, and zinc, as well as significant quantities of iron, silver, copper and gold that are prohibited from leaving the country during the Song Dynasty (Quan 1972, 501–504; Tuotuo et al. 1985: chapter 186 Treatise on Food and Commodities viii 4566; NCUCH et al. 2017b, 419–508). If these items were part of the tribute trade, the Song government would have considered them as legitimate trading activities. However, research suggests that the Southern Song Dynasty actively encouraged private maritime trade and attracted overseas merchants, while maintaining a highly negative attitude towards tribute trade (Huang 2019). Furthermore, during the reign of Emperor Xiaozong (1162–1189 AD) in the Southern Song Dynasty, only three countries — Chenla, Srivijaya and Champa — were involved in the maritime tribute trade, and the tribute was relatively small (Zhou 2004, 185; Ma 2011: chapter 332 The Four Barbarians, part four 9164; Xu 2014: chapter Barbarians iv 9806–9833). Therefore, after excluding the possibility of tribute trade, the metal artifacts carried by Nanhai No.1 should be considered contraband.

The prohibition on taking copper coins out of the country was one of the strictest regulations of the Song Dynasty, and was reiterated multiple times. During the reign of the Northern Song Emperor Renzong (1022–1063 AD), it was decreed that "anyone taking more than 1000 copper coins out of the country would be executed"; "any merchant or foreigner intending to travel to the South China Sea region could take a maximum of 500 copper coins as travel expenses, those who exceeded this amount would be punished"; and, "the Shibosi and the coastal military were ordered to frequently and strictly inspect and supervise to detect any illegal activities" (Zhang 1992, 412). The Southern Song Dynasty also maintained the rule that individuals could not carry more than 500 copper coins. During the reign of Emperor Xiaozong, it was ordered that "foreign seafaring merchants may not carry more than 500 copper coins per person" (Xie 2002, 414). As of now, approximately 30,000 copper coins have been found on Nanhai No.1,Footnote 3 enough to sentence 30 people to death. Moreover, these 30,000 coins are not all the coins that were on the ship at the time. During the sinking and in the subsequent burial at sea, some coins were scattered outside the ship and not all were recovered. Therefore, the actual number of coins carried at the time may have been even greater. Calculated on the basis of the crew of Nanhai No.1, which did not exceed 60 people (Huang and Feng 2021), the average number of copper coins carried per person has exceeded 500, which constitutes smuggling behavior.

While it may be debatable whether carrying copper coins is smuggling, there is no doubt that the silver and ironware loaded on Nanhai No.1 constitute smuggling. Emperor Xiaozong issued a decree prohibiting the trade of gold and silver by foreign ships (Tuotuo et al. 1985: chapter 35 Emperor Xiaozong 678). The Song people believed that trading ceramics, tea, and alcohol with foreign countries was harmless, as it involved exchanging useless goods for useful ones, but gold, silver, copper coins, and copperware were all valuable prohibited items (Xu 2014: chapter Penal Law ii 8372). Iron was an essential material for military weapons at the time, and its export was prohibited by the Northern and Southern Song Dynasties (Su 1986, 889; Li 2004, 11435–11462). Therefore, the 300 kg of silver and 124 tons of iron cargo carried by Nanhai No.1 were undoubtedly goods intended for export and thus contraband smuggling.

In the concurrent trade between the Southern Song Dynasty and the Jin Dynasty, despite the high vigilance of the Southern Song, the smuggling of precious metal items such as gold, silver, and iron to the Jin Dynasty by merchants and officials continued unabated (Wei 2023, 80–81). By comparison, trade between the Southern Song Dynasty and the countries of the South China Sea lacked the tension of military or political factors. Regulations were relatively lenient, leading to widespread smuggling. Cases of collusion between officials and merchants to transport contraband were not uncommon (He and Qiu 2000). This also increases, to a certain extent, the possibility that the silver, iron and other metal goods carried on board Nanhai No.1 may have been smuggled out as contraband.

Method of Trading Metal Goods

The iron artifacts recovered from Nanhai No.1 are comparable in weight to ceramic. With such a large amount of contraband loaded on the upper deck of the ship, it would have been difficult for Nanhai No.1 to leave the port under the existing inspection system of the Shibosi. According to Huang’s (2019) study, Song Dynasty merchants had two possible methods of loading smuggled goods when leaving the port. First, they could bribe officials of the Shibosi and local authorities at the port. Historical records document instances where "officials were corrupt and unjust, often accepting bribes without conducting thorough inspections" and where "inspectors would merely glance and then walk away, never truly knowing the vast amount of goods hidden inside"(Bao 2006). Secondly, the Shibosi officials or local authorities at the port may have turned a blind eye to merchants loading prohibited goods in order to increase tax revenues. Historical records state: "To ensure the annual tax revenue, the Shibosi would annually commissioned wealthy merchants to engage in maritime trade during the winter months. Those who were reluctant to participate were forced to do so. Given the official mandate behind this trade, even if contraband was being transported, no one dared reveal it, and officials lacked the bandwidth to investigate further" (Xu 2014: chapter Penal Law ii 8372).

However, it would have been almost impossible for a ship carrying such a massive quantity of metal contraband as Nanhai No.1 to evade the triple inspection of the Shibosi officials, maritime transport inspectors, and local judges before setting sail. Moreover, under Song Dynasty laws, officials who neglected their duties during inspections faced severe punishment, such as "indefinite suspension," while "those who did not neglect their duties during their tenure would be promoted," making it highly unlikely that they would have overlooked such a large amount of contraband (Xu 2014: chapter State Offices xliv 4207–4215). Therefore, the contraband found on Nanhai No.1 was unlikely to have been loaded onto the ship as a result of bribery or official negligence in order to increase tax revenues.

The lower deck of Nanhai No.1 carried legal goods, while the upper deck contained a large quantity of prohibited ironware, with other prohibited items such as copper rings and coins hidden in ceramic cosmetic boxes, suggesting a deliberate attempt to conceal them. It is likely that the ship initially loaded smaller, easily concealable prohibited items such as gold, silver, and copper by making false declarations. Then, after obtaining legitimate trade permits, the ship passed through port inspections and document checks and left the port under the jurisdiction of the Shibosi, ostensibly in compliance with regulations. During the Song Dynasty, however, it was common for ships to be loaded with prohibited ironware after leaving port (Huang 2019). Merchants would typically accumulate contraband, such as copper coins, and hide them in coastal houses, remote sea locations, or small boats stationed several miles away, waiting for the inspection to be completed before quietly transferring the goods to their ships without arousing suspicion (Bao 2006). The Song Dynasty, with its extensive coastline and numerous overseas trading ships each year, combined with the lucrative profits from smuggling metal goods, made it almost impossible to eliminate smuggling activities (Bao 2006). According to historical records such as the Zhufanzhi, smuggling of metals, including gold, silver, and iron, was widespread during the Song Dynasty, especially during the prosperous trade period of the Southern Song Dynasty (Zhao 1996, 34–43, 55, 141–143).

By first obtaining permission to sail legally and then loading a large quantity of prohibited goods, Nanhai No.1 was able to apply for and obtain official permission to sail normally. In addition, the goods brought back on the return trip could enter the Chinese domestic market legally. This approach allowed traders to make substantial profits from smuggling while ensuring they could legally complete the procedures for selling their imported goods upon return, thus enjoying both the convenience of complying with the regulation and the benefits of circumventing it.

The contraband found on Nanhai No.1 includes not only hidden metal items such as copper coins and rings hidden in ceramic containers but also a large quantity of ironware placed on the upper deck of the ship. This suggests the possibility that both the practice of carrying a small amount of contraband before departure and loading a large quantity after departure may have occurred simultaneously. The manner in which Nanhai No.1 departed remains a subject for further discussion. While it cannot be ruled out that it was a pure smuggling vessel, it is more likely that it functioned as a regular merchant vessel that later loaded contraband.

A Shift in Trading Patterns

Metalware smuggling continued throughout the Song Dynasty. Examination of surviving shipwreck material reveals different patterns of trade or smuggling of metalware at different periods, possibly reflecting shifts in the Song government's approach to trade organization. By analyzing the cargo loading methods of shipwrecks, including Intan (Flecker 2002), Cirebon (Liebner 2014), Nanhai No.1 (NCUCH et al. 2017b), and Quanzhou Bay (Quanzhou Maritime Museum 2017), Li (2020a, 2022) proposes the existence of two different maritime trade models in the South China Sea during the Song Dynasty. In the tenth century, represented by Intan and Cirebon, the trade in bulk commodities was driven by individual or a few wealthy merchants or merchant organizations (probably government agencies) with substantial assets, and they were sold to a single destination. In the later period, such as the time of Nanhai No.1, maritime trade evolved into a profit-oriented endeavor dominated by private merchants, including not only wealthy merchants or those with official backgrounds but also sailors and small traders from lower social classes (Li 2020a, 2022).

The increasing complexity of trading groups, the variety of goods traded, and the diversity of trading locations led to a decrease in government control over overseas trade, making it more difficult to regulate the smuggling of metal goods. This is tentatively confirmed by the types and quantities of metal artifacts recovered from shipwrecks in the South China Sea region. Early shipwrecks such as Intan (Flecker 2002) and Cirebon (Liebner 2014, 183–184) yielded relatively few metal objects, while later shipwrecks such as Nanhai No.1 (NCUCH et al. 2017b, 419–518; Li 2021), Huaguangjiao No.1 (Meng 2018), and Java Sea (Mathers and Flecker 1997, 77–95; Flecker 2003) yielded a greater abundance of metal objects. In fact, the value of the ironware on Nanhai No.1 far exceeded that of the other main cargo, such as ceramics (Li 2021). Although no specific estimates have been made, the value of the 190 tonnes of ironware found on the Java Sea shipwreck is likely to be far greater than that of the ceramics carried on the same ship. These findings can also be seen as evidence of a shift in trade patterns.

We believe that there are two main factors contributing to this phenomenon. First, during the Song Dynasty, there was a noticeable decline in government control over foreign trade. The flourishing development of the commodity trade brought significant economic benefits, not only attracting more officials seeking to profit from it, but also significantly empowering maritime merchants economically. In pursuit of excessive profits, these merchants increasingly engaged in the smuggling of metal goods such as ironware, exacerbating the situation. Even in official and private records of the Song Dynasty, metal goods and other contraband were considered primary commodities in trade exchanges. The expansion of the commodity trade also exacerbated the prevalence of corruption among officials (He and Qiu 2000). Together, these changes led to a decline in government control over maritime commerce.

The second factor is the deliberate tolerance of illicit foreign trade by the Song government, primarily to increase tax revenues. Due to antagonistic relations with northern regimes such as the Liao and Jin, and particularly after Jin's victory over the Northern Song government, which compelled its relocation from the Yellow River Basin at Bianjing to the Yangtze River Basin at Lin’an, the initial financial situation was extremely dire. As a result, there were vigorous efforts to expand foreign trade, with foreign trade revenues becoming a crucial pillar of support, especially in the later stages of the Southern Song period when tax revenues reached unprecedented heights. According to the researches by Tong (1980) and by Lü and Liu (2013), the net revenues of just two local maritime trading offices in Guangzhou and Quanzhou accounted for about one-fifth of the total annual revenues of the Southern Song Dynasty, becoming a vital support for its survival and development. As a result, historical records show that the government deliberately overlooked and even encouraged illegal smuggling activities by merchants in order to increase tax revenues (Xu 2014: chapter Penal Law ii 8372).

The various factors outlined above may have collectively contributed to a shift in the Song Dynasty's foreign trade pattern from state-led to profit-driven private enterprise, resulting in an escalation of smuggling activities. This transition is evident in both the historical record and the artifacts recovered from shipwrecks, which corroborate each other.

The Industrial Chain of Metal Trade

During the Song Dynasty, iron products were an important commodity for foreign trade. The discovery of numerous iron pots and iron bars aboard Nanhai No.1 is an example of this type of important commodity (Figs. 3, 5). Similarly, Huaguangjiao No.1 also yielded a significant amount of iron bars (Meng 2018), although the exact weight could not be estimated due to the lack of complete salvage. In addition, the main cargo of Java Sea consisted of ironware (190 tonnes), including iron pots and iron bars, most of which had corroded and solidified into concretions (Mathers and Flecker 1997, 77–95; Flecker 2003). These three shipwrecks occurred within relatively close time periods (all during the Southern Song Dynasty), and the types and shapes of iron artifacts recovered from archaeological excavations were largely similar. This indicates the widespread practice of exporting and smuggling ironware during the Southern Song Dynasty, and demonstrates the flourishing iron trade in the South China Sea region during the Song Dynasty.

Fig. 5
figure 5

a Iron billets for weapon manufacturing; b Iron pots

Full size image

Iron mining and metallurgy were well-developed industries during the Song Dynasty (Qi 1999), particularly concentrated in southern China, including Zhejiang, Fujian and Guangdong provinces (Wang 2005), which provided favorable conditions for the production and export (or smuggling) of iron goods. Iron products, often in the form of semi-finished goods, were not only essential for production and daily life in the Song society, but were also highly sought after by users in overseas regions (Meng 2018).

Analysis of the metal artifacts recovered from Nanhai No.1 has revealed the beginnings of a metal processing and manufacturing industrial chain during the Song Dynasty (Yang 2018a; Li 2020c, 2021). Nanhai No.1 yielded a significant quantity of bundled iron bars and sheets, which make up the bulk of the iron artifacts on board. These iron bars and sheets exhibit a wide range of types, with inconsistencies in shape, length, width and thickness even within the same bundle of artifacts. Based on the analysis, it is determined that these iron artifacts were semi-finished products that had not yet undergone final processing (Wan et al. 2016; Yang 2018a). Yang (2018a) suggests that these semi-finished iron artifacts had a low carbon content and good ductility, making them suitable for further forging. Based on the shapes and characteristics, Yang (2018a) speculates that the bar-shaped iron products may have been billets for weapons, probably not in the typical Song Dynasty style, but similar to foreign blade styles (NCUCH et al. 2017b, 518; Fig. 5). These semi-finished iron products, manufactured in the Song Dynasty, were transported abroad for final processing by local craftsmen. This approach served to minimize costs and facilitate maritime transport, leaving the final and simplest processing steps to the craftsmen at the destination (Yang 2018a). The latest research indicates that the copper rings found on Nanhai No.1 may also have been traded as semi-finished products, similar to iron billets, and then undergo final processing at their destination (Chen et al. 2024). This demonstrates the prevalence of semi-processed goods in metal trade in the South China Sea region.

Luxury items such as gold and silver artifacts, as well as gold and silver currency, were also found aboard Nanhai No.1. These discoveries include approximately 300 kg of silver ingots and silver artifacts, along with over 400 g of gold leaves and gold fragments (excluding gold jewellery) (Li 2020b, c, d, 2021; Figs. 6, 7). In addition, similar gold leaves with identical shapes and stamped inscriptions have been found in Southeast Asian regions, such as Khao Chai Son in southern Thailand (Sukkham 2014–2015) and Kota Cina on the island of Sumatra, Indonesia (Milner et al. 1978; McKinnon and Treloar 1980; McKinnon 1984, 84–88, 315). These archaeological findings suggest that gold currency was commonly used in trade within the South China Sea region. Research also suggests that Southeast Asia adopted a gold and silver standard currency system early on to facilitate international bulk trade, particularly under the influence of Arab and Indian trade networks (Huang and Liu 1997).

Fig. 6
figure 6

a The silver concretion unearthed from the midsection of C11. b Sketch of the silver concretion unearthed from the midsection of C11. c Five silver ingots with slightly different shapes and sizes

Full size image
Fig. 7
figure 7

a–e Shredded gold; f Small disk-shaped gold; g Remnant of ring-shaped gold; h-i Shredded gold foil; j A gold leaf with inscriptions in Chinese characters

Full size image

Nanhai No.1 also yielded approximately 2400 g of gold jewellry, including four gold rings without gems, six gold belt accessories, ten pairs (20 pieces) of gold earrings, three gold necklaces, and seventeen pieces of bar-shaped gold ornaments (Fig. 8), as well as copper scales and copper weights used to measure precious metals (Li 2021; Fig. 9). A copper weight unearthed in the Saudi port of Al Serrian in a context contemporary with Nanhai No.1 showed identical features, suggesting that both East and West Asian regions used similar scales for precious metal transactions during the Song Dynasty (Li 2020c). Li’s (2020c) analysis of the cultural elements, artistic styles, processing traces of gold jewellry, and the Chinese weighing instruments recovered from Nanhai No.1 suggests that the artifacts recovered from the wreck provide a comprehensive chain of evidence. The gold jewelry found aboard Nanhai No.1, some with gemstone inlays, indicates that some were exported as finished products, while others were exported as semi-finished products to the Arabian Peninsula or the Persian Gulf region, forming a supply chain for the production and sale of luxury gold goods (Li 2020c).

Fig. 8
figure 8

a A gold ring without gem; b A belt accessory without gem; c Bar-shaped gold ornaments; d Gold earrings; e–f Gold necklace

Full size image
Fig. 9
figure 9

Copper weights, scale and weighing pan

Full size image

Research suggests that the gold ornaments unearthed at Khao Chai Son, while not as diverse as those from Nanhai No.1, share certain stylistic and decorative similarities, blending the indigenous styles of Song Dynasty China with influences from regions beyond China, such as West and South Asia (Ding 2022). At Kota Cina, remnants of gold jewelry found near a South Indian-style stupa exhibit Indian or Javanese characteristics. The discovery of gold foil stamped with Chinese characters (probably part of a gold leaf) suggests that Chinese artisans may have produced gold items tailored to local styles and demands, with craftsmanship that is difficult to distinguish from local, Indian, and even Javanese styles (McKinnon 1984, 84–88).

The archaeological findings and research results mentioned above indicate that the metal goods of the Song Dynasty, including iron and gold products, catered to the demands of Southeast and West Asia. A burgeoning chain of metalworking industry began to take shape, covering vast regions from the South China Sea to West Asia. The economic operations associated with Nanhai No.1 are integral to an extensive network of trade, playing a crucial role and serving as a central hub in ensuring the seamless satisfaction of trade needs among different stakeholders.

In addition to metals such as iron, gold, silver, and copper, a significant quantity of tin ingots has been found on shipwrecks in the South China Sea region dating from the 10th to the thirteenth centuries (Ridho and McKinnon 1998; Flecker 2002, 82–83). Tin could serve as a general equivalent, even as currency, and could be used in the production of tinware, bronze alloys, and metallic coinage (Yang 2018b). These finds of metal artifacts paint a vivid picture of the metal trade along the maritime routes of the Song Dynasty. Despite official bans imposed by the Song government, the volume of trade may have declined, but driven by considerable demand and economic incentives, these bans failed to dampen the enthusiasm of those involved in the trade.

Problems Caused by Metal Smuggling

The thriving overseas trade brought enormous economic benefits and tax revenues to the Song government. However, due to inadequate government control, it also led to persistent problems, most notably a shortage of currency (Qiao 1990). Although copper was considered the key to national wealth for coinage, the establishment of trade management institutions in cities such as Quanzhou and Guangzhou attracted foreign merchants, resulting in a flourishing currency trade. Over time, prohibited items such as gold, silver, copper coins and copperware flooded foreign markets due to long-standing customs and frequent exchanges (Xu 2014: chapter Penal Law ii 6564–6567).

The Song Dynasty had long enforced a ban on copper, especially as the outflow of copper coins and the destruction of coinage exacerbated the shortage of currency. Copper, as the main material for minting coins, was strictly controlled by the central government (Xu 2014: chapter Penal Law ii 6564–6567). The private ownership, manufacture and trade of copperware was expressly prohibited, and various measures were taken to prevent the leakage of copper coins and other prohibited items in overseas trade (Bao 2006; Ma 2011: chapter 9 Study of Coins part two 229–263; Xu 2014: chapter State Offices xliv 4207–4215). However, despite repeated bans by the Song government, the copperware trade and overseas trade continued unabated (Xu 2014: chapter Penal Law ii 6564–6567).

Cases such as the discovery of copper rings and coins hidden in a cosmetic box of Nanhai No.1 are not unique, as similar discoveries have been made in previous underwater archaeological surveys in China (Yang 2018a). The large quantity of Chinese ironware found on shipwrecks, such as Nanhai No.1, Huaguangjiao No.1, and Java Sea, indicates the unsatisfactory enforcement of the Song iron ban. Historical records from the Songshi also document this phenomenon, stating: "Gold, silver, copper, and iron were transported overseas by sea vessels, resulting in significant losses, particularly in the case of copper coins. Despite strict legal prohibitions, smuggling activities became increasingly rampant. Merchants, driven by greed for greater profits, resorted to transporting contraband metals, while corrupt officials accepted bribes and turned a blind eye to criminals. These shortcomings ultimately proved difficult to eradicate" (Tuotuo et al. 1985: chapter 186 Treatise on Food and Commodities viii 4566).

During the Song Dynasty, long-term bans on metal commodities and currency were enforced. With the opening up of foreign trade, the Song government benefited from the profits of the international market. However, they also faced the challenges of trade costs and risks. In fact, the power of the international trade market, like an invisible hand, often transcended administrative boundaries and national territories, incorporating different races and interest groups into the system of international maritime trade. The resulting common interests and relationships weakened the stringent measures and actions of the Song government, rendering the currency ban and other metal prohibitions ineffective, and even remaining largely on paper without proper implementation (Li 2012).

The discovery of large quantities of smuggled metal on shipwrecks in the South China Sea region during the Song Dynasty, as well as Song Dynasty coins found in Southeast Asia, South Asia, and West Asia (Yao 1998, 147–154; Nge 2005, 140; Peng 2007, 296–298, 333), fully demonstrate that the circulation of metalware was an inevitable result of the significant expansion of overseas trade. This also suggests that the Song government's efforts to enforce the metalware ban were unsuccessful, leading to adverse consequences such as the currency shortages that affected the economy and livelihoods of the Song Dynasty (Qiao 1990). However, the frequent trade exchanges during the Song Dynasty, including the smuggling of prohibited metal goods, not only brought substantial economic benefits to Chinese private traders but also contributed significantly to the Song Dynasty's financial income amidst ongoing confrontations with northern regimes. Objectively, it also promoted the exchange of goods, culture, and technology between China and neighboring countries in the South China Sea region.

Conclusion

The archaeological finds from Nanhai No.1 provide crucial physical evidence for further analysis of the maritime trade history during the Song Dynasty. The large quantity of metalware unearthed, especially iron, silver, gold, and copper, indicates the presence of smuggling activities on the ship. In transporting these smuggled goods, merchants may have used methods such as false reporting, mixing smuggled goods with legal goods, and evading official supervision to engage in illegal trade in the international market. This discovery highlights the phenomenon of traders risking breaches of national laws in pursuit of high profits. Additionally, after evaluating the bulk commodities of Nanhai No.1, it was found that the value of ironware and silver ingots far exceeded that of ceramics, and the value of gold items also exceeded one-third of the value of ceramics. This provides important insights into understanding the commodity value, cargo significance, trade patterns, and profit composition of overseas trade during the Song Dynasty.

An increasing number of archaeological shipwreck sites in the South China Sea region reveal the prosperity of the metal trade during the Song Dynasty. A comparative analysis of trade patterns across different periods suggests a transition in the foreign trade pattern from one primarily led by the government and official merchants to one dominated by private merchants. This transition coincided with a diversification in the sources of merchant groups, as well as an expansion in the variety of traded goods and trading locations. As a result, government supervision and control of overseas trade declined, making it more difficult to regulate metal smuggling activities. This shift can be attributed to changes in the government's organization of trade and its deliberate tolerance of certain smuggling activities in order to increase tax revenues.

Research into the industrial chain of the metal trade suggests that iron products were important export goods during the Song Dynasty. Custom-made semi-finished gold and iron products indicate the development of a complete supply chain for the design, manufacture and sale of metals, covering a vast area from the South China Sea region to West Asia. These discoveries enhance our understanding of maritime trade during the Song Dynasty and provide valuable archaeological evidence for exploring the commercial activities and trade networks of the time.

The prosperity of overseas trade during the Song Dynasty was accompanied by persistent illegal metal trading activities. Prohibited items such as Chinese copper coins and copper products flooded the international market, causing a coin shortage in the Song territory. Despite numerous government decrees, private traders continued to flout regulations in pursuit of profit. This highlights the inadequacy of government control and the strong influence of the international market on trade. Metal smuggling in the Song Dynasty became a complex game of national economic gain, national security, private interests, and government regulation, with profound implications for the Chinese economy and society. Throughout the Song period, efforts to stem the outflow of metal goods proved ineffective, exacerbating contemporary economic challenges. Yet this illicit trade also served the social demands of Southeast Asia and other regions (e.g. West Asia), facilitating the exchange and dissemination of goods, technology, and culture across ancient territories.