The term comes from the early Roman Calendar and the expression, "Beware the Ides of March" was supposedly said to Julius Caesar.
According to the About website:
The ominous warning, "Beware the Ides of March," originated with the Roman ruler, Julius Caesar, who was assassinated on the Ides of March - March 15, 44
B.C.E. If you've heard the ominous warning, then it's most likely due to William Shakespeare and his play, Julius Caesar.
The warning itself was made famous in Shakespeare's play on Julius Caesar, when an unidentified soothsayer tells Caesar, who is on his way to the Senate (and his death), "Beware the ides of March." Caesar replies, "He is a dreamer; let us leave him. Pass."