 The Sumerians spoke a language isolate, but a number of linguists have claimed to be able to detect a substrate language of unknown classification beneath Sumerian because names of some of Sumer's major cities are not Sumerian, revealing influences of earlier inhabitants.However, the archaeological record shows clear uninterrupted cultural continuity from the time of the early Ubaid period (5300–4700 BC C-14) settlements in southern Mesopotamia.The Sumerian people who settled here farmed the lands in this region that were made fertile by silt deposited by the Tigris and the Euphrates.