Babylonia was formed out of the combined territories of Akkad and Sumer, with the Akkadian language evolving to form the language of Babylonia and the Sumerian language falling into disuse.
Written records are not found in the language of Akkad until the time of Sargon of Akkad. While Sargon is traditionally cited as the first ruler of a combined empire of Akkad and Sumer, more recent work suggests that a Sumerian expansion began under a previous king, Lugal-zage-si of Uruk[?]. However Sargon took this process further, conquering many of the surrounding regions to create an empire that reached as far as the Mediterranean Sea and Anatolia.
In the later Assyro-Babylonian literature the name Akkadu appears as part of the royal title in connexion with Sumer; viz. non-Semitic: lugal Kengi (ki) Uru (ki) = sar mat Sumeri u Akkadi, "king of Sumer and Akkad," which appears to have meant simply "king of Babylonia."