Ides of March is March 15.
According to Borgna Brunner, Editorial Director, Information Please at Pearson Education, “The term Ides comes from the earliest Roman calendar, which is said to have been devised by Romulus, the mythical founder of Rome…the Roman calendar organized its months around three days, each of which served as a reference point for counting the other days: Kalends (1st day of the month), Nones (the 7th day in March, May, July, and October; the 5th in the other months), Ides (the 15th day in March, May, July, and October; the 13th in the other months), The remaining, unnamed days of the month were identified by counting backwards from the Kalends, Nones, or the Ides.” (Source: Infoplease)
Wikipedia, the most ubiquitous – if not the most authoritative – source on everything, states, “The term Ides of March is best known as the date that Julius Caesar was assassinated, in 44 BC, the story of which was famously dramatised in William Shakespeare's play Julius Caesar.
It adds, “Caesar was assassinated on the Ides of March, 44 BC, after declaring himself dictator of Rome, for life. According to a near-contemporary biographer, Caesar summoned the Senate to meet in the Theatre of Pompey on the Ides of March. A certain soothsayer warned Caesar to be on his guard against a great peril on the day of the month of March which the Romans call the Ides; and when the day had come and Caesar was on his way to the senate-house, he greeted the seer with a jest and said: "The Ides of March has come," and the seer said to him softly: "Aye, Caesar, but not gone."
“As the Senate convened, Caesar was attacked and stabbed to death by a group of senators who called themselves the Liberatores ("Liberators"); they justified their action on the grounds that they committed tyrannicide and were preserving the Republic from Caesar's alleged monarchical ambitions."(Painting)
An amazing factoid that I discovered serendipitously on a BBC website is that it was on this day (March 15) in 1876 test cricket was born.If you have time and internet, scholarship's seemingly a piece of cake!