Ides of March

Ides of March is the name of the 15th day of March in the Roman calendar. The word Ides comes from the Latin word "Idus" and means "half division" especially in relation to a month. It is a word that was used widely in the Roman calendar indicating the approximate day that was the middle of the month. 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.(source)

"On the Ides of March the plebs celebrated the Annae festum geniale Perennae (corresponding to the chief day of the Hindu Holi) near the banks of the Tiber (Ovid, Fasti iii. 523-42, 675-96). Rome was, therefore, empty of the lower classes. Is this why the nobles chose the day for the assassination of Julius Caesar?"
"The Ides of March"
C. M. Mulvany
The Classical Review, Vol. 19, No. 6 (Jul., 1905), p. 305 (source)