Across the Shatt al-Arab floodplain in southern Iraq, more than 7,000 substantial earth ridges span an area of approximately 800 km²—traces of a once-extensive irrigation system that supported large-scale agriculture. Until recently, the precise origins and reasons for the system’s eventual abandonment remained uncertain. A new article by Peter Brown of the Radboud Institute for Culture and History, published in Antiquity (Cambridge University Press), sheds light into this remarkable and long-overlooked landscape.
Rebellion and urban growth
Historical texts record a slave rebellion in the region in the late 9th century CE. Scholars have often suggested the ridges visible in the landscape today were created by these slaves and that the hard work required to erect the ridges and farm this landscape may even have been what provoked the rebellion. In the same period, the neighbouring city of Basra seems to have reached a peak in terms of population and commercial activity. Farming a large area would have been necessary both to feed the large urban population as well as to produce agricultural products for export to other cities and overseas.
Scientific breakthrough
Recent archaeological fieldwork conducted through a collaboration between researchers at Radboud University, the Netherlands, the universities of al-Qadisiyah and Basra, Iraq, and the universities of Newcastle and Durham, United Kingdom, have significantly enhanced our understanding of this agricultural landscape. Researchers retrieved soil samples buried deep within several of the ridges. These samples were then analysed using a scientific method called Optically Stimulated Luminescence dating. This method allows the calculation of the length of time since individual grains contained within soils were exposed to sunlight. In the case of the ridges in southern Iraq, the results of this analysis give the date when these ridge features were under construction - or when the soils within them were buried and hidden from sunlight.
A long-term agricultural legacy
The results of this research reveal that the soils sampled in the ridges accumulated shortly after the slave rebellion recorded in the texts, in some cases likely just several decades afterwards. The close association in time between the sampled ridges and the events described in the historical texts means that some of these landscape features very likely existed before the rebellion. The results, therefore, strengthen the link with the slave rebellion which had often previously been assumed but without definitive proof. Perhaps more importantly, however, the results also reveal that the ridge features continued to accumulate for several centuries in the aftermath of the slave rebellion. This means the slave rebellion itself was not the ultimate cause of abandonment. At this stage, it is impossible to say exaclty why this large agricultural system was abandoned but possible explanations include political and economic disruption caused by the invasion of the Mongols in the 13th century, the impact of plague in the 14th century, and climatic change - which could have resulted in a reduction in the amount of water available for farming in the region.
In the media
The research is also receiving international attention. The Independent, a British online newspaper, wrote an article about it.