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, the Cucuteni–Trypillia culture of the Carpathian Mountains, 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.