Geophysical Prospecting on Soils in Mesopotamia: From Mega-Cities in the Marches of Southern Iraq to Assyrian Sites in the Mountains of Kurdistan

Abstract

Enrichment of magnetic minerals in the topsoil and thus enhancement of magnetic susceptibility in archaeological layers and soils, the so-called “Le Borgne effect” is a quite common and a widespread property of the majority of soils worldwide. This effect is widely regarded as the main fundament and plays a crucial role for a successful magnetometer prospecting of most case studies for prospecting worldwide (Le Borgne, Ann Geophys 11:399–419, 1955; Mullins, J. Soil Sci 28: 223–246, 1977; Fassbinder et al., Nature 343(6254):161–163, 1990; Fassbinder & Stanjek, Archeol Polona 31:117–128, 1993; Jordanova, Soil magnetism. Applications in pedology, environmental science and agriculture. Academic Press, Amsterdam, 2016). Case studies both, in the wetland and marches of the Shat el Arab in Southern Iraq as well as on some sites of mountain areas of Kurdistan however, show that this effect plays a minor role in Mesopotamia (Fassbinder & Asandulesei, Peshdar Plain Proj Publ 1:112–119, 2016; Fassbinder et al., Magnetometer prospection of neo-Assyrian sites in the Peshdar Plain, Iraqi-Kurdistan. In: 12th international conference of archaeological prospection, vol 12. Archaeopress, pp 70–72, 2017a, Geophysikal research in the Bora Plain: magnetometer prospection at the Dinka Settlement Complex and Gawr Miran, 2016, vol 2. Peshdar Plain Project Publications, pp 18–32, 2017b, The 2017 magnetometer survey of the Dinka Settlement Complex, Iraqi Kurdistan, vol 3. Peshdar Plain Project Publications, pp 19–30, 2018, Geophysical prospection campaign 2019: magnetometry and Earth Resistance Tomography (ERT) at the archaeological site of Ur, Iraq. Unpublished report Directorate of Antiquities, Iraq, 2019a, Venice in the desert: Archaeological geophysics on the world’s oldest metropolis Uruk-Warka, the city of King Gilgamesh (Iraq). In 13th international conference on archaeological prospection, vol 13, pp 197–200, 2019b, Petiti et al., Zeitschrift für Orientarchäologie Bd 15:120–162, 2023). Here we present a variety of further soil magnetic, rock magnetic and physical properties of archaeological sediments and features, explaining the success, failure, and pitfalls of these prospecting projects. While in the southern Iraq induced magnetisation and the variance in composition of mudstones dominates magnetic anomalies, the selected case study from Iraqi-Kurdistan is predominantly determined by the natural remanent magnetisation of rocks.

1 Introduction

Geophysical prospection at an archaeological site in Iraq was to our knowledge introduced for the first time by Italian and German researchers in the 1960s and 1970s (Ratti, 1971; Lanza et al., 1972; Becker, 1977; Hrouda, 1978). Due to the political situation of Iraq under the regime of Sadam Hussein (from 1978 to 2003) access to regions in the northern Iraq and in particular to Iraq-Kurdistan was nearly impossible and archaeological field research came to an abrupt end. Archaeological research resumed in these regions only after 2010. On the other hand, field research on a multitude of archaeological sites in southern parts of Iraq was still possible but nevertheless was very limited due to the political circumstances during and after the first Gulf War from 1980 to 1988. Although many archaeological excavations took place during the period from 1980 to 2000 but none of them included geophysical prospection in their research program. This is due also to the fact that in the 1980s “large area” magnetometer prospecting was still not as common as it is nowadays.

Helmut Becker and Jörg Fassbinder then undertook the first caesium magnetometer prospecting in Iraq in April 1989 on the Assyrian site Assur (Andrae, 1938; Becker, 1991; Fassbinder et al., 2024). It was Barthel Hrouda, (Director of the Institute of Near Eastern Archaeology LMU Munich, (in a cooperation with the Bavarian State Dept. of Monuments and Sites), was among first archaeologists working in the Near East who started his new excavation project in Assur by magnetometer prospecting of the site. Already soon after, Sadam Hussein invaded Kuwait and the second Gulf War began so that further geophysical prospecting could not follow up in Iraq.

It was then only in the year 2001 and 2002 when there was the chance to introduce archaeological geophysical methods by a magnetometer test measurement in Uruk-Warka (Becker & Fassbinder, 2001; Fassbinder et al., 2005; Ess et al., 2006). In a cooperation with the German Archaeological Institute (DAI) we were able to conduct a magnetometer survey of ca. 20 ha. Further work then again was interrupted by the American invasion of Iraq in 2003. Since 2016 however it became more safe and easier to access the southern part of the country for further prospecting (Fassbinder, 2020; Ess & Fassbinder, 2021). Meanwhile, archaeological geophysics were widely accepted as important toolkit by Near Eastern Archaeologist and there are large ranges of sites, which where currently prospected magnetically by teams e.g. from France, Italy, Czeck Republic, England, Russia and many others (Nadali & Polcaro, 2015; Lambers et al., 2019; Campbell et al., 2018; Darras & Vallet, 2021; Jankowski-Diakonoff et al., 2021). From a multitude of archaeological sites that where prospected by our team in Iraq-Kurdistan, we present here the case study of Neo-Assyrian site Gird-I Bazar. From the southern Iraq, we show examples from our long-term project Uruk-Warka (Andrae, 1935), the Sumerian City of Ur (Woolley, 1934–1976) and Charax-Spasinou (Hansman, 1967) (Fig. 1). Further test-measurements done at Fara Shuruppak resembles magnetically the results from Uruk-Warka, will soon presented elsewhere (Hahn et al., 2022).

Fig. 1

Map of Mesopotamia and Iraq. Archaeological sites in Iraq which where prospected by the Munich team is marked in red

Magnetometry for archaeological prospecting using total-field caesium-magnetometers was developed and refined at the Bavarian State Department of Monuments and Sites in a close cooperation with the Geophysics Institute of the Ludwig-Maximilians-University Munich since the late 1970s. The caesium magnetometer probes, compared to commercial models, provide us by up to 100 times higher resolution (Breiner, 1965; Mathé et al., 2009; Fassbinder, 2015, 2017). These types of instruments, adapted to the specific requirements of archaeological prospecting, must be carried manually approximately 30 cm above the ground. Unlike vector magnetometers, such as fluxgate and SQUID magnetometers, any kind of magnetic metal near the caesium magnetometer will disturb and restrict its high sensitivity. Test measurements with a wheeled devised four-canal fluxgate magnetometer system failed (Parsi et al., 2019). Ground conditions at Uruk, Fara Suruppak and Charax and partly in Ur, are soft, muddy or dusty soils and sometimes combined with uneven terrain. Such conditions make utterly impossible to use a wheeled prospecting system. They will both stick in the soft mud or sand and damage the archaeological features.

2 Magnetometer Prospecting in the Mountains of Iraq-Kurdistan (Northern Iraq)

2.1 The Assyrian “Settlement” Gird-i-Bazar

The settlement complex Gird-i-Bazar in the Peshdar Plain was discovered occasionally in 2014 by the construction of a chicken farm. Already in 2013, a fragmented cuneiform tablet found by a farmer nearby at Qalat-I Dinka, turned out to be a legal document of Neo-Assyrian time from the year 725 BC. Karen Radner—following a suggestion from Jessica Giraud, who found Neo-Assyrian pottery during an extended surface survey at these areas—visited the site 2015 and decided to start a new research project, called the “Peshdar Plain Project” with the goal to investigate Neo-Assyrian monuments in the region. Already in the summer 2015 the Munich Prospecting team together with Andrei Asandulesei (University of Iasi) followed the invitation of Karen Radner to start a magnetometer prospection within the framework of this project. Meanwhile the site was prospected very widely and extensively by different geophysical prospecting methods (Fassbinder & Asandulesei 2016; Fassbinder et al. 2017a, b; 2018; Radner et al., 2016–2020).

2.1.1 Magnetometer Prospection

The magnetometer prospection completed in 2019 revealed a large settlement complex which covers an area of more than 500 × 700 m in size (Fig. 2). From the results of the survey, it seems clear that we are dealing with a single-phase site. In the centre, we detected traces of destruction by a mud-slice, but no further indication of a second archaeological phase became visible. The fundaments of houses, fireplaces and kilns show up by a very clear and high contrast to the adjacent soil. This is due to the highly magnetic gabbro and serpentine rock inclusions of the gravels (usually 10–20 cm in diameter) used as foundation material of the mudstone walls (Herr, 2017). Although there was a great variety of rocks from sediments such as limestone, dolostone and breccia, the occurrence of these few serpentines and gabbro’s dominates the magnetic signal (see magnetic susceptibility values Table 1). In consequence, the magnetogram reveals a single-phase settlement and beside the destruction by an ancient mudslide, no further indication of second phase is detectable. However, first excavations inside the fence of the chicken farm from 2015 (Kreppner et al., 2016) proved already that the magnetogram at the area (eastern trench) does not show any traces of the ground map (see Fig. 3a, b). Further “in situ” analysis of the fundaments in this specific part of the excavation by the kappa meter proved that here serpentine and gabbro rock where absent. Obviously, the builders of these houses used another quarry for gravels for their foundations.

Fig. 2

Gird-I Bazar, Dinka lower town. Magnetogram of the settlement complex

Table 1 Kappa values of a selection of identified gravel rocks from Gird-i Basar and Qalat i Dinka. Note that the typical gravel rocks showed a great variety in the content of magnetic minerals (measured by kappa meter SM30, ZH-Instruments, CZ)

Fig. 3

Gird-I Bazar: Magnetogram top and excavation results bottom. The magnetogram is dominated by the occurrence of different gravels that were used. In the northern part magnetic gravels from gabbro and serpentine yield clear features—in the south-east the fundaments are composed of limestone and dolostone and thus remains invisible in the magnetogram image

The majority of archaeological features in Gird-i Bazar have rock foundations of houses that are composed by serpentine and gabbro’s and are thus very sharp and clearly identifiable in the magnetogram. However, the same layers and features can be also nearly invisible if their fundaments are solely composed of limestone and dolostones like in the right part of the magnetogram (Fig. 3). That means from the magnetometer survey we cannot exclude further features and buildings in the area since they could be invisible due to the less contrasting material. Moreover, test excavations and deep soundings at the area of Gird-i Bazar and electrical resistivity tomography (ERT) measurements undertaken in 2019 on the site reveal further deeper archaeologic layers beneath the Neo Assyrian settlement complex (Parsi & Fassbinder, 2020). No traces of these layers where detectable with the magnetometer survey. Surface surveys of pottery by Jessica Giraud (Giraud, 2016) however indicate the existence of features from older periods. From the magnetometer measurements, although they seemed to be perfect and clear, we cannot deduce that they reveal all the features, and it cannot be excluded that this single-phase settlement overlays and masks some older layers and features at the site. In the measured area of ca. 500 × 500 m, we found at least four lightning strikes identifiable by their typical star shaped and highly magnetic traces (Maki, 2005; Fassbinder, 2017).

3 Magnetometer Prospecting in the Marshland of Southern Iraq

3.1 Uruk-Warka

Uruk-Warka, already a megacity more than 5000 years ago, was first and foremost the centre for a multitude of technical innovations. This includes the construction of irrigation canals, the invention of plastic mortar, astronomy, writing, literacy and numeracy. It was also scene of action humankind’s oldest surviving saga, the famous “Epic of Gilgamesh”. First systematic excavations and archaeological research at Uruk-Warka took place already since 1912/13 (Andrae, 1935). By more than 40 campaigns, the German Archaeological Institute (DAI) have revealed the ruins of this metropolis. About 40,000 residents inhabited Uruk already by 3000 BCE, in an area of ca. 5.5 km². The diameter of the city is 2.6–3.1 km; the enclosing wall has a length of ca. 11 km. Meanwhile surface surveys, satellite image and air photo analysis, geophysical prospection of six campaigns as well as excavations and cuneiform tablet texts have confirmed the presence of canals, houses, temples, and gardens even outside the city wall (Ess & Fassbinder, 2019, 2021).

It is self-evident that modern archaeological research into such an enormous site cannot be restricted anymore to excavation and archaeological surface survey. In 1999, it was first Margarete van Ess who came up with the idea to undertake a large-scale magnetometer prospecting of the site. First test were done already 2000 and 2001 following up until 2021 by meanwhile six campaigns of magnetometer surveys.

Magnetometer prospecting in Uruk was initiated 1999 by the archaeologist Margarete van Ess (director of the DAI in Baghdad) and carried out by the Munich prospecting team in 2001–2002. Further measurements resumed after the Iraq war from 2003 in 2016, and continued in 2018, 2019 and 2021. The first geophysical survey started in the southwestern part of the city, focused on an area north of the Sinkashid Palace and in the south and north in- and outside the city wall. Meanwhile we surveyed from north to south more than 100 ha (> 1 km²⁾ which gives at least a sufficient insight into the organisation of the western part of the city (Fig. 4).

Fig. 4

Uruk Warka. Satellite image from 2005 fused by the magnetogram images from 2001 to 2021 (grid-size of magnetograms 40 × 40 m)

A large canal passes this area to from north to south and includes smaller canals and its branches, a harbour and settlement areas east of Sinkashid palace and settlement areas southwest and east of the palace. In the south, the survey area covers the southern city wall, bringing to light construction details of the monumental city-wall, nearby gardens, and fields as well as a water gate. In the south, outside the city, a large burial ground and a huge monumental building complex with related associated harbour was brought to light.

Meanwhile after several campaigns the magnetogram images provides us with a detailed insight into settlement areas, gardens, and fields close to the city wall, as well as a network of canals that obviously served as the main arteries of Uruk. This network of waterways and canals cross the city from north to south and makes the city quarters accessible, but also provide water for the irrigation of gardens inside the enclosed city. The main canal that is seen in the eastern part of the magnetogram for a length of meanwhile ca. 2400 m. It is 15–20 m wide and 3 m deep and, at several points, slightly smaller canals branch off to the west. Left and right of the canal we traced settlement areas, divided by the smaller canals that led to fields and gardens (Fig. 5). Canals of three or four different widths, the smallest belonging to the field irrigation systems, can be distinguished. The central part of the magnetically scanned area is characterised by two different main features. In the south, a large structure, running east west, seems to accompany the canals into the city centre. A similar shorter structure some metres to the west obviously blocks part of the main canal. None of these hydraulic constructions are visible neither from the air nor from the ground, which is very flat in this part of the city. However, they seem to control or guide the water flow and the canals. Here a selective excavation could determine the date and the nature of these structures. In the south, the city wall and a small canal crossing the city wall can be seen (Fig. 6). Here, the course of the city wall and, at regular intervals, its bastions known from previous excavations and documentation elsewhere in the city, are clearly visible. The high intensity of the signal over parts of the wall on its inner and outer faces seems to indicate the presence of fired bricks, a detail that was not known before. Recent excavations brought to light that these bricks were composed with admixture of fragmented pottery (Fig. 9). It is also apparent that the fortification complex was constructed suing more separate walls than were previously known, and that the canal circling the city ran just outside it. The entire wall system was nearly 40 m wide. The wall itself, with its inner and outer shells of bricks, is ca. 9 m thick, an observation that corresponds to the excavation findings. Further details about Uruk’s structure are provided by the magnetogram of the north and southwest gate, which are nearly 15 m wide and can be interpreted as a floodgate, where the inner city’s main and central canals flowed in and out through the wall. On the outside, the gates were flanked by towers and walls that were strengthened with fired bricks (Fig. 6). Downstream of the floodgate, a small side canal branches off to the southeast, expanding roughly midway in front of a large building of fired bricks into a small harbour-like structure (Fig. 8).

Fig. 5

Uruk-Warka. Magnetogram showing details of the city wall, bastions, gardens, ancient field furrows and irrigation systems

Fig. 6

Uruk-Warka. Magnetogram details of the southern water gate, the sluice system and pipeline beneath the wall

Archaeological features showed extremely high magnetic anomalies and were characterised by sharp magnetic contrasts to the adjacent sediments. Structures become magnetically visible due to different composition of mudstones and due to the thermo-remanence of burned features. Sarcophaguses and coffins on a burial ground in the south of the city (Fig. 7) show up both as positive and or negative anomalies due to different stage or temperature of burning (for more details, see Fassbinder et al., 2019b; Petiti et al., 2023). The waterways and canals show up by clear “negative” anomalies. This implies that heavy and magnetic minerals where already separated from the sediments before the water enters the city. Normally one would expect that like in ancient canals and palaeochannels magnetic minerals concentrates and forms positive magnetic anomalies due to the enrichment of heavy magnetic minerals by water separation (e.g. Babaev et al., 2019).

Fig. 7

Uruk-Warka. Magnetogram details of a cemetery with coffins of different magnetic compositions, generating both positive and negative anomalies

Although resistivity values were extremely low due to the high salt concentration (ca. 10%) of the sediments, the first tests with ERT in the spring season of 2019 provided good results with respect to measuring the exact depth and extent of some archaeological features, such as the mudstone city wall and the shape and extent of the canals and harbours (Fig. 10).

Further work will involve a detailed analysis of the magnetograms, supplementary earth resistance or seismic surveys, satellite remote sensing, UAV surveys, topographical information. All these results, combined to the findings from targeted excavations, will allow a closer insights into the development, the structure and the functions of the city, even without large and costly excavation. The magnetometer survey hopefully will be continued and will offer a comprehensive picture of the structure of Uruk through time (Figs. 5, 6, 7, 8, 9 and 10).

Fig. 8

Uruk-Warka. Magnetogram details of the southern palace and adjacent harbour

Fig. 9

Uruk-Warka. Magnetogram details from the monumental city wall. Parts of the U-shaped bastions and mudstone wall seemed to be from baked mudbricks. Excavations however revealed that these mudstones where composed by pottery shards and not by baked bricks

Fig. 10

Uruk-Warka. Magnetogram of the main canal of the city and associated data of ERT-profile. ERT results over the canal with dipole-dipole configuration and 0.75 m electrode spacing. (a) Left: The result of the robust inversion method, which shows the shape of the canal by its high resistivity values. (b) Right: The result of the Smoothness-constraint inversion method, which shows the sedimentation layers inside of the canal

3.2 Ur

Ur, the city of moon god and “Home of Abraham”, was founded in the fourth millennium BC and is one of the most prominent cities in Mesopotamia beside Uruk-Warka and Babylon (Woolley, 1934–1976). There is the hypothesis that the occupation ends by a flood, formerly thought to be the one described in Genesis. The size and area of the inner city enclosed by a wall (ca. 1200 × 800 m) is much smaller than the city of Uruk. Nonetheless, in the next (Early Dynastic) period, Ur became the capital of southern Mesopotamia under the Sumerian kings of the first dynasty of Ur (twenty-fifth century BC). The last king, who left his traces at both Ur and Uruk, was the Achaemenian Cyrus the Great (sixth century B.C.), whose inscription on bricks was found in recent excavations. The cities survived until the reign of Artaxerxes II (third century B.C.). It was perhaps at this time that the Euphrates changed its course. Ur was finally abandoned with the breakdown of its irrigation system as the fields were reduced to desert. In contrast to Uruk, the remains and ruins of Ur are predominantly made from baked bricks and the infrastructure consist of a network of roads and footpaths instead of canals like in Uruk (Fig. 11).

Fig. 11

Ur. Satellite image (Bing-maps) fused by the magnetogram image of 2019 (grid-size of magnetograms 40 × 40 m)

The objectives of the geophysical exploration in Ur were to map the horizontal extent of the city wall, its vertical dimensions, and to acquire information related to the stratigraphic layering between the two main wall structures. Therefore, magnetometer and ERT surveys were combined at this site also.

Wide areas of the surface of Ur are simply not accessible or suitable for magnetometer prospecting. This is due to deep erosion canals and due to the old and extensive excavations from Woolley (1934–1976). In any case, the magnetometer surveys covered an extensive area. The results were dominated by high thermo-remanent magnetisation of baked brick. The debris of these bricks cover wide areas of the surface and thus sometimes hide or overlay the layout of archaeological features.

An ERT profile was laid out perpendicular to the direction of the wall, which had already been revealed by the magnetometer results. The results suggested that the wall is preserved to a height of ~1 m, which match Woolley’s records. The width of the inner and outer wall was estimated to be ~4 and 2 m respectively (Parsi et al., 2019). The water content in the soil is a limiting factor that potentially can affect ERT interpretations. Soil moisture content was monitored with the repeated ERT measurements over the same profile for a whole day and the tomographic data was also supported with the collection of direct soil moisture, temperature, and conductivity measurements over the city wall with a Time Domain Reflectometry (TDR) instrument. The preliminary results showed a maximum moisture content change of about 10 vol% and plays only a minor role for the resulting data. Other ERT profiles with different electrode spacing targeted the location of the harbour to verify its existence, which was already suggested by the magnetometer results. The left side of the map in Fig. 12 shows the wall. The width of the harbour is around 15 m and its depth about 8 m. According to the result of the ERT, the wall could be made of baked bricks. This information also matches the evidence from the archaeological records. Overall, ERT measurements turned out to provide a suitable complementary prospection method to magnetometry. It delivered reliable information on the depths of archaeological features that are situated in clayey, salty and waterlogged soils. ERT also demonstrated potential to detect mudstone constructions in the adjacent clay and mud.

Fig. 12

Ur. ERT profile and related magnetogram over the harbour wall in Ur (electrode spacing 0.5 m, dipole-dipole configuration)

3.3 Charax

The ancient city of Charax Spasinou dates from the Seleucid to the Sasanian period (305 B.C. to 651 A.D.). It is situated in southern Iraq ca. 40 km north of Basra, between the rivers Tigris and Eulaios, at the modern location Jebel Khayaber. The city was founded by Alexander the Great and named Alexandria. After its destruction by a flood, it was re-founded in 166/165 BC by the Seleucid king Antiochos IV and re-named Antiochia. Later, a great flooding again destroyed the site. It was then rebuilt under Hyspaosines and named Charax Spasinou (ancient Greek for ‘palisade of (Hy)spa(o)sines’). Due to its favourable location Charax became a very important harbour in the Persian Gulf area and a major trading point between India and Babylonia, supplying goods further up to the Mediterranean (Campbell et al., 2018). Charax was first identified with Jebel Khayaber in 1965, when distinctive ramparts with an average height of 4 to 6 m were documented (Hansman, 1967).

In 2016, the University of Manchester, the University of Konstanz, and the Iraqi State Board for Antiquities & Heritage started a large prospection project to document and protect the ancient city of Charax Spasinou. The aim was to integrate satellite imagery analysis, walkover survey, and targeted excavations to reconstruct the city layout, its chronology, and document its state of preservation for site management purposes.

In the same year, the Munich prospecting team carried out a first survey to prove the suitability of magnetometry to detect buried structures embedded in the swampy and waterlogged soils of the Shat el Arab area in collaboration with Jane Moon and Robert Killick and the Iraqi State Board for Antiquities & Heritage, (Lambers et al., 2019). The former river course of the Karun has heavily eroded the southern part of the city, beyond the riverbed now visible in satellite images, but the results of the 2016 survey indicated that some parts of the city could still have survived. During the Iraq-Iran War in 1980–1988, the whole area of the ancient site was intensively used battleground and left traces of vast destruction in the field. The site is still contaminated and covered by a multitude of deep trenches from tanks, but also contaminated by metallic rubbish, destroyed weapons and military equipment.

To our surprise, this first magnetometer survey provided extraordinary results with respect to the high and clear contrast of the magnetogram image (Fig. 13). Although the site was highly contaminated by metal objects, the salty and wet environment seems that served to induce a fast corrosion of metallic iron to rusty weak magnetic iron oxide such as goethite ferrihydrite and lepidocrocite, thus not detectable anymore by magnetometers.

Fig. 13

Charax-Spasinou. Magnetogram fused by a satellite Image (Google-Earth) Scintrex SM 4G-Special Caesium magnetometer in a duo-sensor and total field configuration (grid-size of magnetograms 40 × 40 m)

The results suggested that the streets of the city centre follow the typical Hippodamian grid system with a grid size of around 161 × 88 m (550 × 300 Attic Ionic feet) which is one of the largest we know from the ancient world (Campbell et al., 2018). Like in Uruk, streets and pathways were paved with pottery shards and thus showed up magnetically by a high and sharp positive anomaly. Two evaluation trenches revealed that the east-west streets at least appear to have been placed over a drainage sub-structure. This was composed of a ditch along at least one side of which three super-imposed rows of re-used storage jars drew the water from the surface (Campbell et al., 2018). The layout of these jars is marked in the magnetogram by a thermo-remanent magnetisation. Such a complex drainage system indicates a high level of investment in urban planning and the importance of resilience against repeated flooding. Unlike situations in Europe e.g. in the Netherlands but also at many sites in Bavaria, swampy or waterlogged soils do not necessarily imply dissolution of magnetic iron oxides magnetite, maghemite or titano-maghemites in the pottery shards as seen in this site.

While the magnetogram of most portions of the site shows a clear picture, some areas show traces of flooding, which eroded the main inner-city structures. In these areas, there are only few faint traces of earlier buildings.

4 Discussion and Conclusion

Unlike the situation in southern Germany and wide areas of Europe, pedogenic enrichment of magnetic minerals in the topsoil is of minor importance with respect to magnetic prospecting on archaeological sites in Iraq.

Remanent magnetisation of rocks and bedrock dominate the magnetic properties of the majority as well as of our selected case studies in Iraq Kurdistan—Muṣaṣir and Dinka in the Peshdar Plain. In the city of Ur the magnetic anomalies are dominated by thermo-remanent magnetisation of bricks kilns, fireplace and pottery kilns.

Induced magnetisation of magnetically contrasting mudstones, of mudbricks and canal sediments in the alluvial plain of the Euphrates River dominate archaeological features in the southern Iraq. Namely, at the archaeological sites from Uruk and Charax the magnetic contrast of mudstone and adjacent sediments depends on the composition of the mudstones. From excavations at Uruk and Charax we knew that mudstones are frequently tempered and composed by pottery sherds. Streets and pathway are paved by pottery shards and thus show up by positive magnetic anomalies.

Archaeological features in swampy and waterlogged salty soil are well visible in the magnetogram image—in contrast to the dissolution of magnetic minerals in the majority of European soils.

The intensity of magnetic anomalies of the archaeological features (total field measurements) has relatively high range of ±30–40 nT.

Magnetic traces of lightning strikes (Maki, 2005; Fassbinder, 2016) are frequent in the magnetograms from Iraqi Kurdistan while such traces but so far rarely reported from measurements in the southern Iraq.

A final observation from our long-term total magnetic field measurements is that the absolute value of the Earth’s magnetic field in Uruk has increased by more than 200 nT from ca. 45. 950.0 nT in the year 2001 to 46,171.0 nT in the year 2021.