Wheels, accounting, bronze - even the class system - have all been attributed to the Sumerians at one time or another. The tomb of Queen Pu-abi at Ur contained the earliest known jewellery, and some time before 6000 bc beer had been invented in the region. And then there was irrigation. Had the Sumerians lived on the Nile, they needn’t have bothered with it. For that river regularly flooded, supplying crops with the nutrients they needed.

But the Tigris and the Euphrates, on which the Sumerians depended, were an unruly pair, bringing drought one year and destruction another. It was this unreliability that drove them to devise a system of dykes and canals to conserve river water and divert it on to their land. Indeed, it may have been the need to manage such an enterprise that led the Sumerians to devise sophisticated systems of social organisation. And success bred success. For centuries, water flowed, crops flourished and the Sumerians were able to spread themselves further and further into the once arid land. Until, that is, the crops began to fail.

They seemed to know that salt was the problem, because after a while, the Sumerians stopped growing wheat and switched to barley, which is more tolerant of high salinity. But it was the beginning of the end.

Inadequate drainage meant that, over the years, traces of salt in the river water had accumulated in the fields. Eventually, the soil was so salty that nothing would grow - not even barley.

Sumerian society ended around 2100 bc. Was this cautionary tale about the dangers of irrigation without proper drainage their final gift to us? Perhaps. But we have been happier to drink their beer than to take their good advice. According to recent estimates, excess salinity now effects at least a third of the world’s irrigated land, and the problem is worsening by the day.