It was Shakespeare that first used the phrase, in his play Julius Caesar, giving the line to a soothsayer who was warning Caesar. The playwright was dramatizing what Plutarch had written , that a seer had told Caesar that harm would come to him no later than the Ides of March.
In case you were wondering, as i was, what “Ides” means, it was not a Latin word for ’15th’. From Wikipedia: The Romans did not number days of a month sequentially from the first through the last day. Instead, they counted back from three fixed points of the month: the Nones (5th or 7th, depending on the length of the month), the Ides (13th or 15th), and the Kalends (1st) of the following month. The Ides occurred near the midpoint, on the 13th for most months, but on the 15th for March, May, July, and October. The Ides were supposed to be determined by the full moon, reflecting the lunar origin of the Roman calendar. On the earliest calendar, the Ides of March would have been the first full moon of the new year (since March was the first month in the earliest Roman calendar.)