The Ides of March fell on the 15th of March. In fact, it once signified the New Year, a key date in the Roman Calendar and was marked with celebrations and rejoicing. In the Roman world, the Ides of each month were sacred to the God Jupiter. On this day the high priest would lead the Ides sheep and goats in procession along the main street to Rome’s citadel. Because it marked the New Year, there was extra revelry and other ritual practices. On this day the Feast of Anna Perenna, a goddess or deity of the circle of the year was also celebrated. From her name we get the term ‘per annum.’ All scores and debts had to be settled by this date. A specially selected man was dressed in goat’s skin and ritually flogged and hounded outside of the city walls to mark the passing from the old year and into the new. He was imbued with all the sins of others and everyone was given a new slate into the New Year. It is from this practice that we get the term ‘Scapegoat.’
After the establishment of the Roman Republic, rulers began exercising control over the calendar, lengthening dates of when they were in power and shortening dates when their rivals were in power. Having won his war with Pompey, Julius Caesar used his position as Rome's chief pontiff to enact a calendar reform in 46 BC and in so doing he changed Rome’s New Year celebration from March 15 date to January. In fact, our modern calendar is very much like the one that Julius Caesar enacted. It had 365 days and 12 months each year and took into account the fact that Earth’s orbit around the sun by adding a leap day every four years.
Ironically on this foreboding day, the Roman Senate conspired to kill Julius Caesar. After ignoring numerous warnings–including those of a seer, Caesar was lured into an ambush and was stabbed 23 times before he died. The expression 'Beware the Ides of March' is first found in Shakespeare's Julius Caesar, 1601. The line is the soothsayer's message to Julius Caesar, warning of his death.