Beware the ides of March
The word Ides derives from a Latin word, meaning to divide. The Ides were originally meant to mark the full moons, but because calendar months and lunar months were different lengths, they quickly got out of step.
The Ides is actually a day that comes about every month, not just in March—according to the ancient Roman calendar. The Romans tracked time much differently than we do now, with months divided into groupings of days counted before certain named days: the Kalends at the beginning of the month, the Ides at the middle, and the Nones between them. In a 31-day month such as March, the Kalends was day 1, with days 2–6 being counted as simply “before the Nones.” The Nones fell on day 7, with days 8–14 “before the Ides” and the 15th as the Ides. Afterward the days were counted as “before the Kalends” of the next month. In shorter months these days were shifted accordingly.
Beware the Ides of March, is a phrase of William Shakespeare, In his play Julius Caesar,
Soothsayer: Beware the ides of March.
CAESAR: What man is that?
BRUTUS: A soothsayer bids you beware the ides of March.
CAESAR: Set him before me; let me see his face.
CASSIUS: Fellow, come from the throng; look upon Caesar.
CAESAR: What say’st thou to me now? speak once again.
Soothsayer: Beware the ides of March.
CAESAR: He is a dreamer; let us leave him: pass.
Sennet. Exeunt all except BRUTUS and CASSIUS
In the play, and in reality , Julius Caesar was indeed assassinated on the ides of March , March 15, in the year 44 B.C.