The Semitic Akkadian language is first attested in proper names of the kings of Kish c. 2800 BC, preserved in later king lists. There are texts written entirely in Old Akkadian dating from c. 2500 BC. Use of Old Akkadian was at its peak during the rule of Sargon the Great (c. 2270–2215 BC), but even then most administrative tablets continued to be written in Sumerian, the language used by the scribes. Gelb and Westenholz differentiate three stages of Old Akkadian: that of the pre-Sargonic era, that of the Akkadian empire, and that of the "Neo-Sumerian Renaissance" that followed it. Akkadian and Sumerian coexisted as vernacular languages for about one thousand years, but by around 1800 BC, Sumerian was becoming more of a literary language familiar mainly only to scholars and scribes. Thorkild Jacobsen has argued that there is little break in historical continuity between the pre- and post-Sargon periods, and that too much emphasis has been placed on the perception of a "Semitic vs. Sumerian" conflict. However, it is certain that Akkadian was also briefly imposed on neighboring parts of Elam that were previously conquered by Sargon.