In B.C.538 a revolt broke out in the south, in the old district of the Chaldaeans, and Cyrus took advantage of it to march into the country.

The Babylonian army moved northward to meet him, but was utterly defeated and dispersed at Opis in the beginning of Tammuz, or June, and a few days later Sippara surrendered to the conqueror.
Gobryas, the governor of Kurdistan, was then sent to Babylon, which also opened its gates "without fighting," and Nabonidos, who had concealed himself, was taken prisoner.

The daily services in the temples as well as the ordinary business of the city proceeded as usual, and on the 3rd of Marchesvan Cyrus himself arrived and proclaimed a general amnesty, which was communicated by Gobryas to "all the province of Babylon," of which he had been made the prefect.

Shortly afterwards, the wife--or, according to another reading, the son--of Nabonidos died; public lamentations were made for her, and Kambyses, the son of Cyrus, conducted the funeral in one of the Babylonian temples.

Cyrus now took the title of "King of Babylon," and associated Kambyses with himself in the government.