The story is set around the fall of Babylon, when on 12 October 539 BCE the Persian conqueror Cyrus the Great entered the city. Its last king, Nabonidus, was captured; his fate is unknown, although he may have been exiled. Several details in the text do not match the known historical facts. Belshazzar is portrayed as king of Babylon and son of Nebuchadnezzar, but was actually the son of King Nabonidus, one of Nebuchadnezzar's successors, who deputised for Nabonidus when the latter was away in Teima, but never became king. The conqueror is named as Darius the Mede, but no such individual is known to history; and the invaders were not Medes, but Persians. John J. Collins suggests this is typical of the story's genre, in which historical accuracy is not an essential element.