Walls of Uruk

The eighty thousand people living in Uruk by 3000 [B.C.E.] sheltered behind walls that were forty feet high and six miles long. Archaeologists estimate these to have cost over five million man-hours to build. The fourth-millennium city occupied about 1.7 square miles, a little bit less than imperial Rome at its peak (2.1 square miles) and larger than classical Athens.

— Land Between The Rivers, Prologue