The south was long thought to be the cradle of civilization until earlier settlements (which probably date from about 7000 B.C.) were found in N Mesopotamia; Jarmo, the earliest of these, was superseded by a succession of cultures: Tell Hassuna, Samarra, and Tell Halaf. Tell Halaf, the most advanced of these early cultures, is famous for Halaf ware, the finest prehistoric pottery in Mesopotamia. It is found at such sites as Nineveh and Tepe Gawra. While these advances were being made in the north, civilization was just beginning in the south, particularly at Eridu. The Al Ubaid culture that followed flourished in both N and S Mesopotamia, at Tell Zeidan and Tepe Gawra (N) and Ubaid, Eridu, and Oueili (S). Irrigated agriculture became widespread, and social stratification developed in this early urban period.