It is speculated by some archaeologists that Sumerian speakers were farmers who moved down from the north, after perfecting irrigation agriculture there. The Ubaid pottery of southern Mesopotamia has been connected via Choga Mami transitional ware to the pottery of the Samarra period culture (c. 5700 – 4900 BC C-14) in the north, who were the first to practice a primitive form of irrigation agriculture along the middle Tigris River and its tributaries. The connection is most clearly seen at Tell Awayli (Oueilli, Oueili) near Larsa, excavated by the French in the 1980s, where eight levels yielded pre-Ubaid pottery resembling Samarran ware. According to this theory, farming peoples spread down into southern Mesopotamia because they had developed a temple-centered social organization for mobilizing labor and technology for water control, enabling them to survive and prosper in a difficult environment.[citation needed]