What does Daniel 9:1 mean?
Biblical scholars place Daniel's initial capture (Daniel 1:1–7) at around 605 BC. He was likely a young teenager at that time. This chapter refers to events happening around 539 to 537 BC: meaning about sixty-six years after Daniel was taken to Babylon. Daniel would be nearing eighty by this time, and still serving as an advisor to rulers in the land of his exile. The presumed timeline would place this vision a few years before Daniel's experience in the lions' den (Daniel 6:1).The identity of "Darius the son of Ahasuerus" is controversial. It's possible he was a sub-ruler appointed by Cyrus the Great. This verse, with others, implies that his leadership was somehow given or appointed (Daniel 5:31). The Medo-Persian empire displaced Babylon when Belshazzar was king (Daniel 5:30). Darius was of royal descent, the son of King Ahasuerus. Inscriptions mention Gobryas, which was likely another name for Darius. Apparently, Cyrus, a highly acclaimed Persian general, made Darius the ruler over the Babylonians, while he continued his military exploits. Darius ruled for only a short time until Cyrus took the reins of government.
This change in rulership seems to have inspired Daniel to research the end of Israel's captivity, especially in the book of Jeremiah (Daniel 9:2).