What was the lingua franca of the Persian Empire?
List of lingua francas
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Aramaic was the native language of the Aramaeans and became the lingua franca of the Assyrian Empire and the western provinces of the Persian Empire, and was adopted by conquered peoples such as the Hebrews.  A dialect of Old Aramaic developed into the literary language Syriac.  The Syriacs, such as the Syriac-Aramaean, Assyrian and Chaldean Christians, continued the use of Aramaic which ultimately evolved into the Neo-Aramaic dialects of the Middle East.