There are inscriptions that evidence the earliest use of the language, dating from the 10th century BC. These inscriptions are mostly diplomatic documents between Aramaean city-states. The alphabet of Aramaic at this early period seems to be based on the Phoenician alphabet, and there is a unity in the written language. It seems that, in time, a more refined alphabet, suited to the needs of the language, began to develop from this in the eastern regions of Aram. Due to increasing Aramean migration eastward, the Western periphery of Assyria became bilingual in Akkadian and Aramean at least as early as the mid-9th century BC. As the Neo-Assyrian Empire conquered Aramean lands west of the Euphrates, Tiglath-Pileser III made Aramaic the Empire's second official language, and it eventually supplanted Akkadian completely.