at Babylon, and while he had thus alienated the local priesthoods, the military party also despised him on account of his antiquarian tastes. He seemed to have left the defense of his kingdom to his son Belshazzar (a capable soldier but poor diplomat who alienated the political elite), occupying himself with the more congenial work of excavating the foundation records of the temples and determining the dates of their builders. He also spent time outside Babylonia, rebuilding temples in the Assyrian city of Harran, and also among his Arab subjects in the deserts to the south of Mesopotamia. Nabonidus and Belshazzar's Assyrian heritage is also likely to have added to this resentment. In addition, Mesopotamian military might had usually been concentrated in the martial state of Assyria. Babylonia had always been more vulnerable to conquest and invasion than its northern neighbour, and without the might of Assyria to keep foreign powers in check and Mesopotamia dominant, Babylonia was ultimately exposed. It was in the sixth year of Nabonidus (549 BC) that Cyrus the Great, the Achaemenid Persian "king of Anshan" in Elam, revolted against his suzerain Astyages, "king of the Manda" or Medes, at Ecbatana. Astyages' army betrayed him to his enemy, and Cyrus established himself at Ecbatana, thus putting an end to the empire of the Medes and making the Persian faction dominant among the Iranic peoples. Three years later Cyrus had become king of all Persia, and was engaged in a campaign to put down a revolt among the Assyrians. Meanwhile, Nabonidus had established a camp in the desert of his colony of Arabia, near the southern frontier of his kingdom, leaving his son Belshazzar (Belsharutsur) in command of the army. In 539 BC Cyrus invaded Babylonia. A battle was fought at Opis in the month of June, where the Babylonians were defeated; and immediately afterwards Sippar surrendered to the invader. Nabonidus fled to Babylon, where he was pursued by Gobryas, and on the 16th day of Tammuz, two days after the capture of Sippar, "the soldiers of Cyrus entered Babylon without fighting." Nabonidus was dragged from his hiding place, where the services continued without interruption. Cyrus did not arrive until the 3rd of Marchesvan (October), Gobryas having acted for him in his absence. Gobryas was now made governor of the province of Babylon, and a few days afterwards Belshazzar the son of Nabonidus died in battle. A