Beware the ides of March

Caesar:
Who is it in the press that calls on me?
I hear a tongue shriller than all the music
Cry "Caesar!" Speak, Caesar is turn'd to hear.
Soothsayer:
Beware the ides of March.
Caesar:
What man is that?
Brutus:
A soothsayer bids you beware the ides of March.
Julius Caesar Act 1, scene 2, 15–19

The ides of March. The fifteenth day of the third month. Not a good day for Julius Caesar, the Roman dictator, as he was assassinated on this date by a group of conspirators including Brutus ("Et tu, Brute?") and Cassius, the instigator of the plot.  The year was 44 B.C. Caesar was 55.