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 4th and 2nd millennia BCE, with the formation of the first city generally dated to around 3500 BCE, at Huaricanga, in the Fortaleza area. From 3100 BCE onward, large-scale human settlement and communal construction become clearly apparent. This lasted until a period of decline around 1800 BCE. Since the early 21st century, it has been recognized as the oldest-known civilization in America, and as one of the six sites where civilization separately originated in the ancient world.