The Nabonidus Chronicle is an Ancient Babylonian cuneiform inscription on a clay tablet. The text tells the story of the rule of king Nabonidus, the last king of the Babylonian Empire and the conquest of Babylon by the Persian king Cyrus the Great. It covers the period of Cyrus’ accession and rule, and ends with the accession of his son, Cambyses. It is the best primary source on the fall of Babylon and Cyrus the Great’s rise to power.
Although the tablet dates somewhere between the 4th and 1st centuries BC, the original text is considered to have been written in the late 6th or early 5th century BC, and is therefore a contemporary (written around the same period) source for the period.
The tablet is significantly damaged and much of it is missing. However there is enough to follow the story. The text is written year by year, giving the events of each year in turn.
Nabonidus, the last king of Babylon, was not in Babylonia for ten years, and instead was attempting to conquer Arabia. In the sixth year, Astyages musters an army and marches against Cyrus, however the army rebel and take Astyages prisoner and hand him over to Cyrus. In the ninth year, Cyrus crosses the river Tigris and kills an unknown king. Finally, in the seventeenth year, Nabonidus returns to Babylon and the Akitu (New Year) festival is able to be celebrated, and the gods appear – however Cyrus attacks and slaughters the Babylonians, Nabonidus flees, but is later captured in Babylon. Cyrus enters Babylon, and there is peace while he speaks. The gods are returned to their places (this is interpreted to mean that the religious statues were returned to the temples, or that the people are able to practice their religions again).
The line-by-line translation of the text from the tablet can be found here: The Nabonidus Chronicle on Livius.com