From N.S. Gill's Ancient/Classical History Glossary
Ides of March assassination of Caesar, by Vincenzo Camucini .Elessar
Definition: The Ides of March was a date on the Roman calendar (Idus Martias) corresponding with our date of March 15. It was a fateful date.
Roman Events on the Ides of March
~ Anna Perenna Festival
In ancient Rome, a festival for Anna Perenna was held on the Ides of March. Ovid, a poet and contemporary of Rome's first emperor, Augustus, wrote a collection of Greek myths in Latin called the Metamorphoses. In this monumental piece of Latin literature, Ovid explains that Anna Perenna was the sister of the tragic, love-sick, suiciding Carthaginian queen Dido, familiar to Romans from the Aeneid, which was written by another Augustan Age poet,Vergil (Virgil).
"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
~ Caesar's Assassination
A more well known occurrence on the Ides of March, in 44 B.C., Julius Caesar was assassinated, at the foot of a statue of Pompey where the Senate was meeting.* Before Caesar went to the theater of Pompey to attend the Senate meeting, he had been given advice not to go, but he didn't listen.
Source of the Expression "Beware the Ides of March"
Because of the assassination and the soothsayer's exchange with Julius Caesar about the dangers he faced in Shakespeare's Julius Caesar tragedy, the Ides of March now signifies a fateful day. Here is the relevant passage:
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
Changing Significance of the Ides of March
1. Before the historical assassination of Julius Caesar, the Ides of March was:
- A division of the calendar based on the phases of the moon.
In some months, the Ides is on the 15th, and in others, it is the 13th. It's supposed to be on the day of the full moon. [See Roman Calendar.]
- March's Ides marked the beginning of the consular year: The two annually-elected Roman consuls took office on the Ides from c. 220 B.C. to 153. From 153 B.C. the consuls began to take office on the Kalends of January (what we call New Year's Day).
2. Even immediately after the historical assassination of Julius Caesar, "the ides of March" could be understood to refer to the assassination. Cicero didn't have to say "the assassination of Caesar." He could assume he would be understood when he alluded to the assassination just by reference to "the Ides of March."
Instead of saying something like the take-down of the dictator means there is hope for the Republic, he wrote -- with complete confidence that he would be understood:
Idus Martiae consolantur.
The Ides of March are encouraging.
~ Cicero Letters to Atticus.14.4 (url = homepage.usask.ca/~jrp638/DeptTransls/CicLetters.html April 19, 44 B.C.)
*See In the Steps of Julius Caesar for why Senate met in the porticus attached to the theater of Pompey that day.