Sumer
Sumer () is the earliest known civilization in the historical region of southern Mesopotamia, modern-day southern Iraq, during the Chalcolithic and Early Bronze ages, and one of the first civilizations in the world along with Ancient Egypt and the Indus Valley. Living along the valleys of the Tigris and Euphrates, Sumerian farmers were able to grow an abundance of grain and other crops, the surplus of which enabled them to settle in one place. Prehistoric proto-writing dates back before 3000 BC. The earliest texts, from c. 3300 BC, come from the cities of Uruk and Jemdet Nasr; early cuneiform script emerged around 3000 BC.
Cradle of civilization
The Norte Chico civilization proper is understood to have emerged around 3200 BC, as it is at that point that large-scale human settlement and communal construction across multiple sites becomes clearly apparent. Since the early 21st century, it has been established as the oldest known civilization in the Americas. The civilization flourished at the confluence of three rivers, the Fortaleza, the Pativilca, and the Supe. These river valleys each have large clusters of sites. Further south, there are several associated sites along the Huaura River. Notable settlements include the cities of Caral, the largest and most complex Preceramic site, and Aspero. Norte Chico sites are known for their density of large sites with immense architecture. Haas argues that the density of sites in such a small area is globally unique for a nascent civilization. During the third millennium BC, Norte Chico may have been the most densely populated area of the world (excepting, possibly, northern China). The Supe, Pativilca, Fortaleza, and Huaura River valleys each have several related sites.