A haul of 154 tablets from Irisaĝrig was returned to Iraq by the British Museum earlier this year Trustees of The British Museum/PA

Thousands of clay tablets have been rescued from smugglers over the past few years, all bearing witness to a lost Sumerian city that was home to a mysterious ancient cult. The tablets show that looters must have discovered the site, and archaeologists are now racing to find it before it is completely ransacked.

Irisaĝrig was a flourishing city that reached its zenith about 4000 years ago. “It was the capital of a major province of the …