Their kingdom came to an end in 550 BCE (or 553 BC according to some sources), when it was conquered by Cyrus the Great, the Persian king of Anshan in south-western Iran. After extending his empire from the Mediterranean to Central Asia, Cyrus turned his attention to Babylonia. The most important ancient sources for his conquest of Babylon are the Nabonidus Chronicle (Nabonidus was the last Babylonian king, and Belshazzar, who is described as king of Babylon in the Book of Daniel, was his son and crown prince), the Cyrus Cylinder, and the Verse Account of Nabonidus—which, despite its name, was commissioned by Cyrus. Cyrus' Babylonian campaign began in 539 BCE, although there were presumably previous tensions. On 10 October Cyrus won a battle at Opis, opening the way to Babylon, and on 12 October "Ugbaru, governor of the district of Gutium, and the army of Cyrus entered Babylon without a battle" (Babylonian Chronicle). Ugbaru is presumably the same person as the Gorbyras mentioned by the Greek historian Xenophon, a Babylonian provincial governor who switched to the Persian side. Cyrus made his entrance into the city a few days later; Nabonidus was captured and his life spared, but nothing is known of the fate of Belshazzar. Historicity of the Book of Daniel The Book of Daniel is not regarded by scholars as a reliable guide to history, and the broad consensus is that Daniel is not a historical figure, the author appearing to have taken the name from a legendary figure of the distant past mentioned in the Book of Ezekiel. While it is a book featuring prophecies, the book that bears Daniel's name is an apocalypse, not a book of prophecy, and its contents are a cryptic allusion to the persecution of the Jews by the Greek Seleucid king Antiochus IV Epiphanes (reigned 175–164 BCE). There is broad agreement that the stories making up chapters 1–6 are legendary in character, that the visions of chapters 7–12 were added during the persecution of Antiochus, and the book, itself, being completed soon after 164 BCE (soon after the reign of Antiochus). Daniel 5 and Daniel 6 belong to the folktales making up the first half of the book. The language of Daniel 5 ("Belshazzar's Feast"), for example, follows ancient Near Eastern conventions which are in some cases precisely those used in Daniel. Daniel 6 ("Daniel in the Lions' Den") is based