Sumer is the earliest known civilization, located in the historical region of southern Mesopotamia, emerging during the Chalcolithic and early Bronze Ages between the sixth and fifth millennium BC. Like nearby Elam, it is one of the cradles of civilization, along with Egypt, the Indus Valley, the Erligang culture of the Yellow River valley, Caral-Supe, and Mesoamerica. Living along the valleys of the Tigris and Euphrates rivers, Sumerian farmers grew an abundance of grain and other crops, a surplus which enabled them to form urban settlements. The world's earliest known texts come from the Sumerian cities of Uruk and Jemdet Nasr, and date to between c. 3350 – c. 2500 BC, following a period of proto-writing c. 4000 – c. 2500 BC.

Caral–Supe was a complex Pre-Columbian era society that included as many as thirty major population centers in what is now the Caral region of north-central coastal Peru. The civilization flourished between the fourth and second millennia BC, with the formation of the first city generally dated to around 3500 BC, at Huaricanga, in the Fortaleza area. From 3100 BC onward that large-scale human settlement and communal construction become clearly apparent, which lasted until a period of decline around 1800 BC. Since the early 21st century, it has been recognized as the oldest-known civilization in the Americas, and as one of the six sites where civilization separately originated in the ancient world.