Possible explanations for the decline of this system might include the Mongol invasion of Iraq which caused significant disruption during the late 13th century.

Our results demonstrate that, while the ridges were likely there at the time of the slave revolt in the ninth century, the soil in the ridges continued to accumulate in the centuries that followed - so this agricultural system has a longer history than was previously assumed.

To provide more certainty, we retrieved samples from within the ridges themselves for analysis using ‘Optically Stimulated Luminescence’ methods. These date the last time individual grains in the soil were exposed to sunlight - when the earth was piled up to form the ridges.

In a few areas, farming still takes place among these ridge features today. These areas capitalize on the Shatt al-Arab river’s tidal effects. Since it lies close to the Gulf, the tide pushes freshwater upriver which can be drawn off via canals to irrigate farmland.

Looking at the areas between these ridge features, we can see traces of canals and in some cases field boundaries - so it is clear that, together, these features form an old agricultural system through which a large area, that is abandoned today, was farmed in the past.

These ridges are massive! Most are around 1 km long, with earth piled up to about 2m high AND there are a lot of them - if you could put each one ‘end to end’, so they formed one continuous line, it would run for over 3000 kilometres! Creating these was a huge amount of work!

Our new article published today in @antiquity.ac.uk focuses on interesting archaeological landscape features in southern Iraq. Groups of long linear earthen ridges sit on the banks of the Shatt al-Arab river in the Basra region, north of the shores of the Gulf… 🧵