Battle of Gaugamela
But Kassites again fought on the Persian side in the Battle of Gaugamela in 331 BC, in which the Persian Empire fell to Alexander the Great, according to Diodorus Siculus (17.59) (who called them "Kossaei") and Curtius Rufus (4.12) (who called them "inhabitants of the Cossaean mountains"). According to Strabo's citation of Nearchus, Alexander later separately attacked the Kassites "in the winter", after which they stopped their tribute-seeking raids.