It was during the campaigns of Alexander the Great, after the Macedonians had overrun the western provinces of the Persian empire, that the eastern Iranian element became especially prominent in the Persian camp. The majority of the eastern Iranian troops had been mustered by Bessus, who after the Persian defeat quickly emerged as the most powerful of the Persian leaders under Darius III. After the assassination of the king, it was Bessus who assumed the royal prerogatives, and retired to his satrapy of Bactria to carry on the struggle against Alexander in eastern Iran. The complex and disturbed succession of the later Indo-Bactrian rulers was to a large extent the consequence of a far-reaching event. After the fall of the Kushan dynasty in AD 225, the provinces of Gandhara, Bactria and Sogdiana passed under the rule of Sasanian governors who bore the title of Kushanshah 'King of the Kushans'. This Persian administration continued until about AD 360.