Ides Of March
This is March 15.
“Ides” was part of a Roman method of keeping a calendar. Rather than number the days, the Romans had three points in the month, and they simply compared the current day to those points. The points were Nones (the 5th or 7th; it depended on the month), Ides (the 13th or 15th), and Kalends (the 1st).
So, every month had an Ides, but the “Ides of March” because more famous because Julius Caesar was assassinated on the Ides of March in 44BC
In Shakespeare’s play Julius Caesar, this exchange occurs:
Soothsayer: Beware the ides of March.
Caesar: What man is that?
Brutus: A soothsayer bids you beware the ides of March.
(This is apparently fictional to the play. There’s no evidence this happened in real life.)
Thus, the Ides of March is associated with danger or a sense of foreboding.
Why I Looked It Up
I had heard the phrase for years.
It recently came up in a book about ancient Rome. A character was born on March 15, though the book is set in 109 BC, so Caesar hadn’t been assassinated yet, so there was nothing notable about the day (other than it fell directly on the Ides).
I also enjoyed a 2011 political thriller called The Ides of March. However, I just re-read the plot summary and can’t figure out how the title is related, except perhaps if the events of the film took place in March. (It’s about a presidential primary race, so that’s quite possible.)