According to the Nabonidus Chronicle, King Ishtumegu (Astyages) “called up his troops and marched against Cyrus, king of Anshan, in order to me[et him in battle]. The army of Ishtumegu revolted against him and in fetters they de[livered him] to Cyrus.” (Ancient Near Eastern Texts, p. 305)

The cuneiform tablets found by archaeologists, though not giving details concerning the exact manner of the conquest, do confirm the sudden fall of Babylon to Cyrus. According to the Nabonidus Chronicle, in what proved to be the final year of Nabonidus’ reign (539 B.C.E.) in the month of Tishri (September-October), Cyrus attacked the Babylonian forces at Opis and defeated them. The inscription continues: “The 14th day, Sippar was seized without battle. Nabonidus fled. The 16th day, Gobryas (Ugbaru), the governor of Gutium and the army of Cyrus entered Babylon without battle. Afterwards Nabonidus was arrested in Babylon when he returned . . . In the month of Arahshamnu [Marchesvan (October-November)], the 3rd day, Cyrus entered Babylon.” (Ancient Near Eastern Texts, p. 306) By means of this inscription, the date of Babylon’s fall can be fixed as Tishri 16, 539 B.C.E., with Cyrus’ entry 17 days later, occurring on Marchesvan 3.