How did Daniel the prophet die?

The answer to this question is simple.  We have no idea how Daniel died.  There is no source which is helpful on this at all.  However, from Daniel chapter six we know that Daniel survived at least a couple of years into the administration of Persia after Babylon was conquered by Cyrus in 538 BC.  We know that Daniel was at least a teenager when he was taken to Babylon in 605 BC (Daniel 1:1).  Therefore, Daniel was at least eighty-two years old when the events of Daniel six happened, so he easily Could have died of the normal processes of old age at this point.  We do not need to consider any kind of extraordinary means of his death.

John Oakes