The city of Mari (modern Tell Hariri) was founded in the middle Euphrates River valley by unknown builders early in the third millennium B.C.E. This part of Syria is a semi-arid region with insufficient rainfall to support dry-farming agriculture. Nonetheless, the founders of Mari established their city on a canal-laced terrace a few kilometers west of the river. They surrounded the city with a circular dike to protect it from floods and connected it to the river through a diversion canal. Behind the dike stood a 6.7-meter-thick (22 feet) defensive rampart. The area is at an important juncture between the main irrigation-based Sumerian city-states along the lower Euphrates River to the south and the dry-farming plains of north Syria along the upper Euphrates and Khabur Rivers, but Mari itself is of no agricultural significance. The position of Mari seems rather to have been determined...