ROME/LONDON (WHTM) — If it wasn’t for William Shakespeare, most of us wouldn’t know what an Ide was.

In Act One, scene two of his play Julius Caesar, Caesar is attending a festival (the Lupercalia, if you want to delve into it), surrounded by admirers and well-wishers. Suddenly, he hears a voice:

Soothsayer: Caesar!

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 say’st thou to me now? speak once again.

Soothsayer: Beware the ides of March.

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The scene goes on a little longer, but you get the idea. Then in In Act III, Scene I, there is another exchange between the two:

Caesar: The Ides of March are come.

Soothsayer: Aye, Caesar, but not gone.

Then Caesar goes off and gets assassinated, uttering his final words ‘Et tu, Brute?’, which is something Shakespeare made up. Thus the phrase “the Ides of March” became part of the English language as a day of evil and ill portent. A fair number of people know the Ides fall on March 15th. And that’s pretty much what most people know about the Roman Calendar.

The ides were just one of three special days in a Roman month. The kalends (from which we derive the word calendar) was the first day of the month, nones was the seventh day of the month, and ides was the 15th day of the month. In the early years of Rome, they used a lunar calendar, and kalends were set at the first sighting of the crescent moon, nones by the first quarter moon, and ides by the full moon.

Now let’s complicate things a little. The early Roman Calendar had months of either 30 or 31 days. March, May, Quintilis, and October had 31 days and were called full (pleni) months. (Quintilis was renamed July after Julius Caesar, but not until after he got bumped off, so we’re kind of getting ahead of ourselves here.) The thirty-day months were referred to as hollow (cavi). The “full” months marked ides on the 15th day, and the “hollow” days marked it on the 13th.

The original Latin word for ides is actually Idus. The Oxford English Dictionary entry on ides says Idus is pronounced with a long U “Idūs”. (Most linguists believe Idus is a loanword from another language, most likely from Etruscan.) The word found its way into Old French, which apparently is where the spelling and pronunciation changed to ides. From there it found its way into English, where Shakespeare rescued it from obscurity.

So is “ides” singular or plural? The OED states “ides” is the plural of “ide”, but also notes “ide” is rarely used. For the most part, “ides” is used as both the singular and plural.

Incidentally, the Soothsayer is not a character invented by Shakespeare. The Bard based his play on Sir Thomas North’s translation of Plutarch’s Lives of the Noble Greeks and Romans, from which he got the exchange “The ides of March are come;” “Yes, they are come, but they are not past.” Another historian, Suetonius, tells us in his De vita Caesarum (The Twelve Caesars) that the Soothsayer’s name is Spurinna, and he is a haruspex, that is, someone trained to divine the future by the examination of entrails of sacrificed animals. The book says “Again, when he was offering sacrifice, the soothsayer Spurinna warned him to beware of danger, which would come not later than the Ides of March.” So Spurinna was someone Caesar knew, and who warned him of danger earlier than he did in the play. Making him a man of mystery who warned Caesar to “Beware the ides of March” only the day before the ides were Shakespeare’s idea. It wasn’t good history, but it was good drama.