You might have heard this strange phrase before, especially if it has to do with bad luck or something spooky, but what does it mean?
It dates back to the time of the Roman Empire, and to the emperor Julius Caesar , who lived from July, 100 BC to the 15th of March, 44 BC (100-44 = 56 years old). According to a historian named Plutarch, a soothsayer, or fortune teller, told Emperor Caesar to "Beware the Ides of March," and that phrase has lived on ever since.
But what did it mean? It was simply the way the Roman people said "March 15."
The term Ides comes from the earliest Roman calendar, which 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. For example, March 3 would be V Nones—5 days before the Nones (the Roman method of counting days was inclusive; in other words, the Nones would be counted as one of the 5 days).
You can read more about the Ides at Infoplease.com .
But the phrase became famous because Emperor Caesar was killed  on March 15, and the message of the fortune teller was retold as part of Caesar's death, kind of like a big "I told you so!"