Nineveh took the lead with 100,000 people by 700 B.C.
Located in Iraq, Nineveh was settled as early as 6000 B.C. By 3000 B.C. it was a major religious center for the goddess Ishtar.
The city really took off around 700 B.C., when the Assyrian King Sennacherib built a "palace without rival." The city was spread over 7 square kilometers, with 15 great gates, 18 canals, and several sections of aqueduct.
Nineveh was besieged and sacked in 612 B.C. as the Neo-Assyrian empire crumbled.