Darius I (Old Persian Dârayavauš): king of ancient Persia, whose reign lasted from 522 to 486. He seized power after killing king Gaumâta, fought a civil war (described in the Behistun inscription), and was finally able to refound the Achaemenid empire, which had been very loosely organized until then. Darius fought several foreign wars, which brought him to India and Thrace. When he died, the Persian empire had reached its largest extent. He was succeeded by his son Xerxes.
In sections 16-20 of the Behistun inscription, Darius tells about the struggle for Babylonia during the civil war. The full text of the inscription can be found here.
After I had slain Gaumâta, the Magian, a certain man named Âššina, the son of Upadarma, raised a rebellion in Elam, and he spoke thus unto the people of Elam: 'I am king in Elam.' Thereupon the people of Elam became rebellious, and they went over unto that Âššina: he became king in Elam.
And a certain Babylonian named Nidintu-Bêl, the son of Kîn-Zêr, raised a rebellion in Babylon: he lied to the people, saying: 'I am Nebuchadnezzar, the son of Nabonidus.' Then did all the province of Babylonia go over to Nidintu-Bêl, and Babylonia rose in rebellion. He seized on the kingdom of Babylonia.note[From Babylonian letters, it is known that Nebuchadnezzar III had started his reign on 3 October 522.]
King Darius says: Then I sent [an envoy?] to Elam. That Âššina was brought unto me in fetters, and I killed him.note[Probably before Babylon was captured.]
King Darius says: Then I marched marched against that Nidintu-Bêl, who called himself Nebuchadnezzar. The army of Nidintu-Bêl held the Tigris; there it took its stand, and on account of the waters the river was unfordable. Thereupon I supported my army on inflated skins, others I made dromedary-borne, for the rest I brought horses. Ahuramazda brought me help; by the grace of Ahuramazda we crossed the Tigris. Then did I utterly overthrow that host of Nidintu-Bêl. On the twenty-sixth day of the month Âçiyâdiya [13 December 522] we joined battle.
King Darius says: After that I marched against Babylon. But before I reached Babylon, that Nidintu-Bêl, who called himself Nebuchadnezzar, came with a host and offered battle at a city called Zâzâna, on the Euphrates. Then we joined battle. Ahuramazda brought me help; by the grace of Ahuramazda did I utterly overthrow the host of Nidintu-Bêl. The enemy fled into the water; the water carried them away. On the second day of the month Anâmaka [18 December 522] we joined battle.
King Darius says: Then did Nidintu-Bêl flee with a few horsemen into Babylon. Thereupon I marched to Babylon. By the grace of Ahuramazda I took Babylon, and captured Nidintu-Bêl. Then I slew that Nidintu-Bêl in Babylon.