The soothsayer’s warning to Julius Caesar was, ‘Beware the Ides of March’… Well apparently, that’s today:
The Ides of March (Latin: Idus Martii) is the name of 15 March in the Roman calendar, probably referring to the day of the full moon. The term ides was used for the 15th day of the months of March, May, July, and October, and the 13th day of the other months.The Ides of March was a festive day dedicated to the god Mars and a military parade was usually held. In modern times, the term Ides of March is best known as the date that Julius Caesar was killed in 44 B.C. Julius Caesar was stabbed (23 times) to death in the Roman Senate led by Marcus Junius Brutus, Gaius Cassius Longinus and 60 other conspirators.
On his way to the Theatre of Pompey (where he would be assassinated), Caesar saw a seer who had foretold that harm would come to him not later than the Ides of March. Caesar joked, “Well, the Ides of March have come”, to which the seer replied “Ay, they have come, but they are not gone.” This meeting is famously dramatized in William Shakespeare’s play Julius Caesar, when Caesar is warned to “beware the Ides of March”…
Wikipedia has more.