The Ides of March is March 15

The Ides of March is celebrated on March 15. The Ides of March festivity is dedicated to the god Mars and a military parade was usually held. In modern times, the term Ides of March is best known as the date that Julius Caesar was killed in 709 AUC or 44 B.C.

From wiki:

* The Ides of March is celebrated every year by the Rome Hash House Harriers with a toga run in the streets of Rome, in the same place where Julius Caesar was killed.

* The Atlanta Chapter of the Dagorhir Battle Games Association hosts an annual spring event at Red Horse Stables on the weekend closest to the 15th of March. The event is appropriately named “The Ides of March”.

* The Temple Hill Association in New Windsor, NY holds an annual dinner in honor of the Ides of March because it is also the day that General George Washington quelled a mutiny of his Officers in 1783.

What Are the Ides?
Another theory, as to why Caesar might have seemingly been ignoring the ominous warning of Spurinna, is that perhaps Julius Caesar got the dates of the warning mixed up. He may have been thinking that the Ides of March fell on the 13th. In the ancient Roman calendar, each of the 12 months had an “ides.” In March, May, July and October, the ides fell on the 15th day. In every other month, the ides fell on the 13th.

The word “ides” was derived from the Latin “to divide.” The ides were originally meant to mark the full moon – but since the solar calendar months and lunar months were of different lengths, the ides quickly lost their original intent and purpose. Using this theory, forgetful Caesar would have been very careful and stayed home on the 13th of March, but on the 15th of March his guard was down.