Introduction
The Rajajil Columns site is situated in the Al Jouf Province of Saudi Arabia (Figure 1). The main site covers nearly 6ha and consists of 54 separate groups of standing sandstone pillars and other stone features (Figure 2). Many of the pillars, originally standing up to 3m in height, are now broken and displaced. Stone-lined features at the base of the pillars may represent burial cairns and a large group of small stone cairns are situated on a hill to the south (Zarins Reference Zarins1979). The site is believed to have extended over a wider zone, but modern agricultural activities have impacted some areas. Previous field studies include site surveys, planning and small excavations at the base of two column groups and a stone feature near the southern periphery (Gebel et al. Reference Gebel and Luciani2016) (Figure 2). Analysis of recovered stone tools suggests activities dating to the Chalcolithic period (fifth millennium BC) with possible traces of both earlier and later activity (Gebel & Wellbrock Reference Gebel, Wellbrock and Chiotis2019). This aligns with the mid-Holocene period, when environmental conditions in the Arabian Peninsula favoured the expansion of mobile pastoralism. Interpretations of Rajajil vary, suggesting it may have served different purposes: as a collective burial ground for dispersed herding communities, a site for astronomical functions, a special location for sociopolitical gatherings and a domestic settlement area (Zarins Reference Zarins1979; Almushawh Reference Almushawh2018; Gebel & Wellbrock Reference Gebel, Wellbrock and Chiotis2019; Kacem Reference Kacem2022). Archaeological research thus far has concentrated on exploring the stone pillar clusters, and a more comprehensive understanding of the function and use of the site through time has remained elusive. Our project extends on previous studies, using geophysical survey to identify associated zones of human activity that may then be validated through ground-truthing, environmental studies and absolute dating. This will contribute to a fuller understanding of this important monumental site across time and through the changing social, economic and environmental conditions that contributed to developing pastoralism in the region. Positioned along an ancient trade route connecting the Red Sea, Levant and northern Arabian Peninsula, this site represents one of the earliest standing-stone monuments associated with pastoralist communities in the region, likely playing a crucial role in emerging social stratification and territorial demarcation.
Figure 1. Location of the Rajajil Columns site. Inset left) GPR survey near RJ-27 complex; inset right) RJ-24 stone complex near site entrance (figure by authors using Esri:ArcGIS).
Figure 2. Images of the Rajajil site: A) drone photograph; B) digital elevation model; C) identified surface features; D) previous archaeological research locations (figure by authors).
Multi-method geophysical survey
In March 2024, we conducted the first exploratory multi-method geophysical survey at Rajajil. A drone provided digital elevation modelling and high-resolution imagery. Subsurface geophysical methods included fluxgate gradiometry (Bartington 601-2), ground penetrating radar (GPR) (Sensors and Software SmartCart, 500 MHz antenna) and a low-frequency multi-depth electromagnetic apparent conductivity/susceptibility meter (GF Industries, CMD-mini Explorer). Five 20 × 20m grid blocks were aligned on a 324° magnetic baseline to encompass two standing-stone clusters (RJ-26 & RJ-27) and an area between them (Figures 3 & 4). Another 10 × 10m grid (4b) was added to the north-east of grid 4a following the identification of two potential stone fire-pit features (Figure 5). Fluxgate gradiometry was conducted in all grids, while GPR was conducted in grids 1, 2 and 4b, and low frequency electromagnetic apparent conductivity/susceptibility in grids 1 and 4b.
Figure 3. A) Geophysical survey grid and identified stone column clusters; B) fluxgate gradiometry results; C) colour contour plot of fluxgate gradiometry results; D) interpretation of fluxgate magnetic responses showing unique responses (a) (1 – rectangular anomaly; 2 –rectangular feature); simple dipolar responses (b) (modern metal debris); complex dipolar responses (c) (modern metal debris and/or burned soil); and monopolar positive responses (d) (figure by authors).
Figure 4. A) Grid 1 location over the RJ-27 column complex; B) fluxgate gradiometry greyscale plot; C–E) apparent conductivity responses, note the large zones of high and low readings, possibly relating to the removal of stone and subsequent infilling with more conductive soils; F–H) apparent magnetic susceptibility responses, note small positive responses likely representing modern metal debris across the site (figure by authors).
Figure 5. A) Drone photograph of grid 4b showing a displaced sandstone pillar (1) and two probable stone fire pits (2 & 3); B) fluxgate gradiometry greyscale plot; C–E) apparent conductivity responses; F–H) apparent magnetic susceptibility responses (figure by authors).
Results
Our research identified several promising anomalies within all surveyed grids. The local sandstone geology is magnetically ‘quiet’ and many monopolar positive responses were recorded in the +1 to +10nT range (fluxgate gradiometry). Such responses may represent infilled pit features and/or low-temperature burning. A strong contrast in such responses characterises the areas surrounding the RJ-26 and RJ-27 columns, with RJ-26 being substantially more magnetically active (Figure 3, grids 4a & 5). Fluxgate gradiometry survey in grid 1 produced intriguing results indicating a rectangular magnetic feature surrounding the RJ-27 stone cluster (Figure 3B & D). The apparent conductive responses achieved through low-frequency electromagnetic survey (both low and high responses) suggest zones where subsurface stone may have been removed during construction activities and subsequently infilled with more conductive soils (Figure 4D & E). Grid 4b produced several geophysical responses in combination with the identification of two probable surface-level fire-pit features (Figures 5 & 6). These included several monopolar positive responses (fluxgate gradiometry) in the range of +1 to +10nT and associated apparent magnetic susceptibility (low frequency electromagnetics). GPR survey in grid 4b also revealed strong subsurface reflections, including a possible curvilinear shape (Figure 6C & F) that may represent a subsurface anthropogenic feature. Two-dimensional GPR radar profiles further indicate substantial modification to the natural geological strata in this grid area (Figure 6D & E), also possibly relating to construction activities.
Figure 6. A) Drone photograph of grid 4b; B) GPR slice view showing locations of strong responses at 0.20–0.25m below surface (2 & 3); C) GPR slice view showing strong reflections at 0.80–0.85m below surface including a possible curvilinear anomaly; D) reflection profile of GPR traverse Line 5; E) reflection profile of GPR traverse Line 22; F) interpretation of curvilinear (a) and other strong GPR reflections (b) at 0.80–0.85m below surface (figure by authors).
Conclusion
Application of multi-method geophysical survey at the Rajajil Columns site has yielded new data relating to underlying geological conditions as well as complex human activities likely connected with construction and use of the site. The variety of subsurface and geophysical responses achieved, and the identification of probable fire-pit features in grid 4b, support the need for more detailed surveys across the site in future. Such surveys, in conjunction with targeted ground-truthing, excavation, artefact and ecofact analyses and radiocarbon dating, may offer a more robust analytical framework for interpreting the nature of human activities associated with this important monumental site and how these may have changed through time.
Acknowledgements
We gratefully acknowledge the support of Dr Jasser Al-Harbash, CEO of the Heritage Commission, Dr Abdullah Al-Zahrani, Director General of the Archaeology Sector, and Dr Ajab Al-Otaibi, Director of the Archaeological Research Department, for allowing and supporting this research by providing the necessary approvals, logistical services including transportation and accommodation and associated travel costs. We also extend our appreciation and special thanks to Mr Khalifa Al-Ruwaili and Mr Khaled Al-Sharari from the Heritage Commission for their exceptional contributions and efforts during our fieldwork.
Funding statement
Research activities were supported by the Heritage Commission of the Kingdom of Saudi Arabia and the Kenneth P. Dietrich School of Arts and Sciences at the University of Pittsburgh.
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