Keywords

1 Introduction

Geophysical methods provide a non-invasive, non-destructive means of studying subsurface archaeological remains, and have been methodologically well developed in archaeology as a new field. In the context of the archaeology of Morocco and Tunisia, geophysical methods have not been consistently applied since their earliest introduction in the 1970s, in marked contrast to their use in geological and hydrological research.

This chapter provides an overview of the history of archaeo-geophysical fieldwork in Morocco and Tunisia. After a synopsis of the history of the region and of the development of geophysical methods in archaeology, we review their application in the fields of archaeology in Morocco and Tunisia.

Geophysical investigations have been conducted as part of pre-excavation assessments to determine where to locate trenches. Also, these methods have been used at ancient and medieval settlements with visible remains to complete their urban layout. North-western Africa has an extensive prehistoric record: Africa as a whole is generally regarded as the cradle of humanity, from which Homo habilis (ca. two million BP) first began to migrate to other continents, and the recent discovery of Homo sapiens at Jebel Irhoud near Marrakesh in Morocco has pushed back the earliest attestation of modern human beings in north-western Africa to ca. 300,000 BP (Hublin et al., 2017).

1.1 Brief Introduction to the History of the Maghrib

The premodern history of the Maghrib, of which Morocco and Tunisia are a part, is conventionally divided into three periods, prehistory, antiquity and the Middle Ages (Laroui, 1970; for Morocco, see Kably, 2011). There are several forms of chronology in place, based on geological epochs, material cultures, and, beginning from antiquity, dated events or periods, like those of ruling dynasties. Such chronologies are often not universal, but are bound to specific contexts and cultural expectations, as with the Neolithic and its implications with a settled way of life dependent upon agricultural and domesticated animals (Barich, 2021). This chronological particularity is also related to the geographical variability of the natural landscape. Even though the complex of mountain chains that form the Rif, Atlas, and Aurès may be viewed as a coherent and unifying geographic feature, diversity in the forms of human adaptation and material culture is evident from prehistory onward (Camps, 1974; Linstädter, 2008).

1.1.1 Prehistory

Prehistory is commonly held to begin ca. one million BP, with the first evidence of Homo erectus, up to the eighth century BCE, when the coasts of north-western Africa were frequented by traders and settlers from Phoenicia (approximately modern Lebanon). This period therefore comprises an extremely long duration of time. Generally speaking, in the Palaeolithic, human begins domesticated fire, used lithic tools, practised funerary rituals and formed the earliest communities, while the subsequent Neolithic saw the domestication of animals, the spread of agriculture and the adoption of a sedentary way of life (Roche, 1963; Strauss, 2001; Hublin & McPherron, 2012; Hublin et al., 2017). The relationships between the Palaeolithic/Neolithic transition, climatic conditions and the particular definitions of material cultures are complicated, as is the question of whether distinctions between post-Neolithic ages like the Copper, Bronze or Iron, which are a basis of periodisation elsewhere in the Mediterranean, should apply (Lucarini et al., 2021). Around the end of the second or start of the first millennium BCE, though, local societies in north-western Africa were adept at mobilising sufficient labour to construct monumental building projects, such as the cromlech at Mzora in Morocco (Bokbot, 2020), and to practise oleiculture and viticulture, as at Althiburos in Tunisia (Kallala & Sanmartí, 2011; Sanmartí et al., 2012; Mattingly, 2016).

1.1.2 Antiquity

Antiquity generally covers the period from the first centuries of the first millennium BCE up to the fifth century CE. During this time north-western Africa attests the earliest phases of urbanisation and the development of political societies, as at Lixus in Morocco and Carthage in Tunisia, which were originally Phoenician colonies (Lancel, 1995; Aranegui & Hassini, 2010). The latter city emerged as an imperial power over the course of the sixth to fourth centuries BCE. In the course of its wars against the Carthaginians, the Roman state became implicated both diplomatically and militarily in the region, and by the mid-first century CE Rome had annexed the coasts and plains of north-western Africa up to the Atlantic coast (Briand-Ponsart & Hugoniot, 2006; Lassère, 2015). The Roman period has traditionally been seen as a period of great economic prosperity, with flourishing urban societies and a high level of rural production (Hobson, 2015). The exportation of products from north-western Africa, such as garum (fish sauce), olive oil and wheat, both for the city of Rome and for the broader Mediterranean economy, as well as the diffusion of ceramic fine ware (African Red Slip ware), represent well the region’s Mediterranean connections. Recently, however, the coherence of such vitality is being revisited, to highlight regional variation (Stone, 2019).

1.1.3 Middle Ages

The division between antiquity and the Middle Ages is situated in the transition between the disintegration of the western Roman Empire in the fifth century CE and the campaigns of the Umayyad Caliphate in the seventh century CE (Leone, 2007; Fenwick, 2013, 2020; Bockmann et al., 2019). The region’s political and military landscape underwent modifications pursuant to conflicts between local kingdoms and external agents, such as Vandals, Byzantines and Arabs. Some urban centres were abandoned or destroyed, such as Simitthu, Carthage and Utica in Tunisia, and Banasa, Zilil and Lixus in Morocco. Other cities continued to be inhabited, however, showing that there was not a complete rupture with the past. That said, the sociopolitical makeup of the region changed considerably, even if gradually, as new political and economic relationships became established (Boone et al., 1990). New centres of power emerged and shifted from one to another, such as at Kairouan, Raqqada, Mahdia and Tunis in Tunisia, or at Fes, Marrakesh and Meknes in Morocco, over the course of the first to sixth centuries AH / seventh to twelfth centuries CE. The most noteworthy changes of the medieval period are found in the domains of religion and language, with the introduction of Islam and Arabic. Such a shift is apparent in importance of the later geographies and accounts of conquest (futūḥ) that form the mainstay of evidence for understanding the political events around the Umayyad conquest, the subsequent rebellions and the birth of states governed by local dynasties (Ṭāha, 1989; Siraj, 1995).

2 Geophysical Surveys in Moroccan & Tunisian Archaeology

While geophysical techniques have been well developed methodologically in archaeology as a global discipline (Aitken, 1974; Atkinson, 1953; Hesse, 1966, 2005; Tabbagh, 1974), the application of geophysics within national and collaborative international archaeological fieldwork projects in Morocco and Tunisia has historically not been as robust. The following sections present a summary discussion of the history of archaeo-geophysical surveys in each country, outlining primary case studies in the application of geophysical methods in archaeological contexts. To be sure, geophysics found ready application in both countries starting in the 1970s, but the frequency of geophysical projects has not been consistent over time, increasing only recently. The application of geophysical methods has largely focused on the investigation of ancient and medieval (Roman and Islamic period) sites, and rarely on prehistoric ones.

2.1 Morocco

In Morocco, the study of cultural heritage falls under the purview of the Framework Law No. 99-12 under the National Charter for the Environment and Sustainable Development Dahir No. 1-14-09 of 4 Jumada I 1435 (6 March 2014) (B.O. No. 6240 of 18 Jumada I 1435 AH, corresponding to 20 March 2014). There are no mentions nor recommendations on the use of geophysical surveys in archaeological heritage documentation and preservation. Since its foundation in 1985, the Institut National des Sciences de l’Archéologie et du Patrinoine (INSAP, the National Institute for Archaeology and Heritage) has been a leading institution for the study of archaeology in Morocco and has undertaken collaborative projects using geophysical methods to investigate archaeological sites. Prior to INSAP, the Service de l’Archéologie (Archaeological Service) was the central institution for archaeological fieldwork in Morocco (Papi, 2006).

Geophysical survey was first used in Moroccan archaeology in the 1970s, with magnetometer and electrical resistivity being the most common methods used. Between 1971 and 1972, at the important medieval centre of Sijilmasa in the Tafilalt region of Morocco, a project of archaeological and ethnological research was directed by the Ludwig Keimer Foundation and the Moroccan government. As part of this work, Boris de Rachewiltz conducted an electrical resistivity survey that revealed a network of underground pipelines that linked vessels and wells buried under the sand (de Rachewiltz, 1972). Another pioneer of geophysical survey on archaeological sites in Morocco was carried out by Alain Kermorvant, who conducted fieldwork under the auspices of the French Ministry of Cultural Affairs (Ministère d’État Chargé des Affaires Culturelles) as part of the Franco-Moroccan excavations at Dchar Jdid (the ancient Roman colony of Zilil). Between 1977 and 1980, Kermorvant carried out a geophysical investigation using magnetometer and electrical resistivity methods (Akerraz et al., 1981–1982). Kermorvant also conducted a magnetometer survey in 1996 under the direction of another Franco-Moroccan collaboration at Banasa, a Mauretanian and Roman period site, where archaeological excavations confirmed the effectiveness of this method for the detection of pottery kilns (Arharbi & Lenoir, 2011). The use of magnetometer surveys to locate potential kilns had already been demonstrated by Patrice Cressier in 1977 at the medieval site of Ain Kerouach, where an electrical resistivity survey was also conducted using with a 1 m electrode-spacing on a Wenner array configuration to locate the walls of the site (Cressier, 1981–1982).

More recent surveys includes the magnetometer explorations at Sidi Ali ben Ahmed (ancient Thamusida), conducted between 1999 and 2001. These surveys were carried out using a fluxgate gradiometer, covering an area of about 14 ha. These surveys were highly effective in detecting the subsurface remains of walls and mapping the buried city, some of the results are presented in Fig. 1 (Cerri, 2008). Kermorvant carried out magnetometer surveys at Kouass in 2009 as part of strategy of targeted excavations (Bridoux et al., 2009). In 2010, Cerri also conducted magnetometer surveys at Lixus (Shoumish), a major urban centre during the Roman period, under a collaborative project between INSAP, Mohammed V University of Rabat and the University of Siena (Italy), to delineate the architecture and built infrastructure of the site (Mascione et al., 2016). Between 2013 and 2017, Francesco Martorella and Laura Cerri investigated the Roman military camp at El Benian, south of Tangier. The results derived from the magnetometer survey (Fig. 2) shed light on the organisation of space internal to the fort in late antiquity (Martorella, 2021). In 2016, electromagnetic surveys were conducted around the eastern gate of the medieval fortress of Ighram Aousser, located south of Meknes (Cozzolino et al., 2016, 2018; Manfredi et al., 2019). The medieval site of Ain Kerouach was revisited in 2018 by researchers from Abdelmalek Essaadi University in Tangier to conduct a magnetometer survey, reassessing the depth of the aforementioned kiln features (Ayad & Bakkali, 2018). Finally, as part of Morocco-American fieldwork in the Loukkos valley under the direction of Aomar Akerraz and Stephen Collins-Elliott, Abir Jrad has carried out magnetometer surveys on several rural sites using the Grad 601-2 magnetometer.

Fig. 1
A schematic illustrates the archaeological structures in Sidi Ali Ben Ahmed, exhibits highly effective surveys for detecting subsurface walls and mapping the buried city.

Archaeological structures revealed by the magnetic anomalies in Sidi Ali Ben Ahmed, ancient Thamusida (Cerri, 2008)

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Fig. 2
A gradiometric map displays a military camp with magnetic anomalies ranging from 9.12 to negative 8.84 nanoteslas. Another map exhibits magnetic anomalies, primary phase magnetic anomalies, visible walled structures, as well as north and west walls, along with a hypothetical moat.

(a) Gradiometric map obtained in the military camp el Benian in Morocco with a range from +9.12 to −8.84 nT (b) Interpretation of the magnetic anomalies (Martorella, 2021)

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2.2 Tunisia

In Tunisia, legislation on cultural heritage can be found under article 94-35 from 24 February 1994 on the Code of Historical Archaeological Heritage and Traditional Arts, which serves to organise and protect Tunisia’s cultural heritage. There are currently no protocols regarding the use of non-invasive methods of geophysical methods.

Geophysical surveys within the domain of cultural heritage have been carried out under the supervision of the Institut National du Patrimoine (INP, National Heritage Institute) of Tunisia and in collaboration with foreign institutions from Poland, Germany, Italy, France and more recently Britain. The first geophysical survey in Tunisia was a microgravimetry investigation of the site of the Roman circus of Carthage in 1972 by a Polish team (Kolendo et al., 1973; Iciek et al., 1974). Carthage was revisited in 2003–2004 for another campaign of geophysical investigation, using both magnetometer and ground penetrating radar (GPR) surveys. This was a collaboration between Tunisia and Italy (Piro & Capanna, 2006). The most recent geophysical survey of this area was conducted in 2015 by a Tuniso-German team, which used three methods: GPR, magnetometer and electric resistivity (Ben Romdhane et al., 2016). The electrical resistivity survey (using a Geoscan Research RM15 resistance meter) did not provide useful results because of the high soil aridity and lack of soil moisture during the survey. The GPR results proved to be the most effective, allowing for the identification of several buried features (Bockmann et al., 2018). The GPR survey was carried out using 200 MHz and 400 MHz central frequency antennas, while the instrument use for the magnetometer survey was a G858 caesium magnetometer. Four caesium probes, spaced 50 cm apart, were placed on a wooden wagon to be towed. This made possible to acquire ten measurements per metre in the direction of travel and four measurements each two metres in the transverse direction.

Geophysical explorations have become more frequent in recent decades in Tunisian archaeology. In 2004, a collaboration was established between the Tunisian INP and the French research program Sisyphe at the Université Pierre-et-Marie Curie Paris VI to conduct a geophysical survey at the site of Ṣabra al-Manṣūriya in Kairouan, one of the capital cities of the Fatmid Caliphate. A combination of methods was used to counteract adverse conditions (such as scrap metal that obstructed results from the magnetometer and high soil salinity that impeded electrical resistivity survey). Results revealed axial alignments of anomalies that were used to target excavations (Cressier & Rammah, 2004).

In 2010, geophysical surveys were conducted at two sites, Chemtou and Utica, in collaboration with the German Archaeological Institute (DAI) and the British School at Rome respectively. Chemtou (the ancient Simitthu) is situated in the governorate of Jendouba in north-western Tunisia. The goal of the GPR survey was to locate the buried walls of the medieval city. Utica, a Phoenician colony and primary urban centre throughout the pre-Roman and Roman period is located at the North of Carthage city. The aim of the survey at Utica was to assess the viability of magnetometer characterisation of the site and the preliminary results proved quite promising as many structures related to the ancient city plan were revealed (Kallala et al., 2010). Since, Utica has been the target of more intensive geophysical survey work. The initial magnetometer survey has been extended and further GPR surveys has been performed in the framework of the Rome’s Mediterranean Ports project of the University of Southampton and the British School at Rome (Hay et al., 2010; Ben Jerbania et al., 2015, 2019; Keay & Hay, 2017).

In 2012, three sites at Carthage (under the supervision of Pr. Aounallah and Dr. Achour), at the North-East of the capital Tunis, and one in Hergla (the ancient Horrea Caelia) at the South of the capital Tunis (under the supervision of Pr. Ghalia), were surveyed (Jrad, 2014). The first one, the Malga archaeological park in front of Carthage-Zaghouan aqueduct, was explored combining electrical resistivity tomography (ERT), magnetometer and seismic surveys. The correlations between the geophysical anomalies allowed the identification of potential archaeological features at ~1 m depth. A magnetometer survey was conducted at the Punic port of Carthage to search for a potential kiln structures as evidence of pottery industry at is area. The third site, a burial ground at Tophet, was surveyed using a G858 magnetometer. The objective of the survey was to understand the magnetic signature of the graves (Jrad, 2014). The last site, the commercial harbour of the city of Hergla, belonging to the governorate of Sousse, was also explored though a magnetometer survey to locate the ancient city walls. In situ magnetic susceptibility measurements of different materials of the walls were also taken using SM30 susceptibility meter and also recorded the archaeological materials at the site to better define magnetic anomalies (Fig. 3).

Fig. 3
A heat map and 3 photos. 1. Maps the dataset obtained from a magnetometer survey conducted in the commercial harbor of the city of Hergla in Tunisia. 2. Aerial and top-angle views of the ancient city wall ruins.

Results of the magnetometer survey of Hergla in Tunisia with some susceptibility measurements (Jrad, 2014)

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In the same year, a Tunisian-German team conducted a geophysical survey at the site of Meninx on the island of Jerba in south-eastern Tunisia, the most important city on the island in antiquity. The German team used a Cesium-Smartmag SM4G-special-magnetometer to cover an area of 120,000 m2. In situ magnetic susceptibility measurements were also taken by a handheld Kappa-meter SM30 (Zh-Instrument) to estimate the magnetic susceptibility of the building materials (Fig. 4) (Ritter et al., 2018; Ritter & Ben Tahar, 2020). The objective of this study was to complete the city plan of Meninx and stablish suitable areas for future archaeological excavation. In 2019, an electrical resistivity survey was carried out also at Jerba island using vertical electrical soundings and ERT to locate remains related to ancient olive oil production infrastructure with promising results (Azaiez et al., 2019).

Fig. 4
A schematic displays the magnetic gradient of Meninx, with devices positioned at various archaeological sites. The scale spans from 4 nanoteslas to negative 4 nanoteslas, providing a comprehensive depiction of magnetic variations across the area.

Magnetic gradient of Meninx (Jerba, Tunisia) and susceptibility measurements from Ritter et al. (2018)

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In 2019, a Tunisian team carried out a magnetometer survey at the archaeological site of Ourazla in Zaghouan (under the supervision of Dr. Ben Romdhane), in eastern Tunisia. Previous rescue archaeological excavations revealed structural remains extending on the course of a modern highway. As a preventive measure, the survey aimed at mapping the total extension of the site. The team was composed by archaeologists from the Heritage Institute of Tunis and a geophysicist from the Water Researches and Technologies Centre. Some preliminary results are shared here. The instruments used was a dual sensor Bartington Grad601-2 magnetic gradiometer which was operated in a scanning mode to do a fast sweep of the study area and locate hotspots where to conduct higher resolution survey. These more detailed surveys were conducted in 40 × 40 m grids collecting data along parallel lines with 1 m line separation and in-line of 1 m, covering a total area of ~1 ha, with a rate of 8 samples/m. The results showed linear anomalies, oriented north-west/south-east and north-east/south, likely to be linked to subsurface remains of wall foundations (Fig. 5). This hypothesis finds support from the fact that part of the alignments detected by the magnetometer survey are known to correspond to a wall within the excavated area. These promising results must necessarily be supplemented and confirmed by additional geophysical survey, and future plans entail the use of parallel and perpendicular ERT profiles to the linear magnetic anomalies to better assess the geometry of these structures.

Fig. 5
A 2-D grid plot of the magnetometer survey of Ourazla in Tunisia. It presents linear anomalies with northeast-southwest orientation.

Results of the magnetomer survey at Ourazla (Zaghouan, Tunisia)

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3 Conclusion

This chapter has sought to present an overview of geophysical applications within archaeological fieldwork in Morocco and Tunisia. The 1970s saw the earliest application of geophysical methods, but with only a score of surveys for archaeological purposes in the preceding half-century in both countries combined. The practice of archaeo-geophysics would therefore appear to have been slow to develop, and is, in some respects, still in its infancy. While geophysical surveys have become more frequent in recent decades, the condition of geophysics in archaeology stands in marked contrast to the regular application of geophysics in other fields, i.e., for both geological and hydrogeological purposes. The extent to which geophysical fieldwork can address prehistoric questions deserves further investigation.

It is clearly desirable to promote and develop geophysical methods as a cornerstone of archaeological fieldwork, especially in the domain of rescue archaeology. Central to this objective is the development of an interdisciplinary pedagogy, to ensure that archaeologists receive training in geophysical methods as part of their university education, whereas currently in Tunisia geophysical methods are taught only to geoscientists. Providing training to archaeologists in geophysical methodologies on a national level will help ensure the place of geophysical surveys as part of the regular process of conducting archaeological fieldwork. Such a goal has several benefits, such as the ability to map entire cities without the need for excavation, or at least reducing the number or extent of excavations to a targeted amount based on specific research questions. Furthermore, fostering training in archaeo-geophysical methods in both Morocco and Tunisia can enhance the frequency of exchanges between both countries and quality of fieldwork to the benefit of protecting our universal heritage.

Finally, bringing the results of geophysical survey into communication with soil analyses will further enhance our understanding of surface anomalies and produce a better reading of the results from geophysics. This domain of research has not yet been sufficiently developed at sites in either Morocco and Tunisia. To be sure, magnetic susceptibilities of archaeological features in Tunisia have been measured, such as with ceramics from surveyed sites at Carthage to find their natural remanent magnetisation (Jrad, 2014), but there have been no results that have combined observation from other type of soil analyses with those from geophysical fieldwork. Addressing this lacuna is imperative. Geophysical surveys using multiple methods that are coordinated with soil analyses will serve to enhance our understanding of past on-site functions (Graham & Scollar, 1976; Cuenca-Garcia et al., 2018), and, being a primary goal of the Soil Science and Archaeogeophysics Alliance (SAGA), deserves more widespread implementation in the Maghrib.