Step 1: Consider the timeline of ancient civilizations. All four options are cradles of early civilizations.
Step 2: Identify the earliest evidence of urbanization. Mesopotamia, the land between the Tigris and Euphrates rivers, is widely credited by historians and archaeologists as the site of the world's first cities. Cities like Eridu, Uruk, and Ur emerged in the Sumer region of southern Mesopotamia as early as the 4th millennium BCE, making it the oldest documented urban settlement. The other civilizations developed urban centers later.