What are the ides of March?

A familiar quotation from William Shakespeare’s play Julius Caesar is ‘Beware the ides of March’. It is spoken by a soothsayer early in the play, and, according to Plutarch, the event actually occurred. The warning portends the eventual assassination of Caesar; but what are the ides of March?

There is nothing inherently unsettling about ides. In the ancient Roman calendar, the ides is notionally the day of the full moon, and falls roughly in the middle of the month: the 15th of March, May, July, and October, and the 13th of other months. While the word can be traced to the Latin idus, the origin is unknown.

Two other similar, less familiar, words also exist in English: nones and calends (or kalends). According to the ancient Roman calendar, nones fall on the ninth day before the ides (so the 7th of March, May, July, and October, and the 5th of the other months), while calends refers to the first day of the month. These three words were also used as markers from which to calculate other dates, hence such expressions as ‘the fifth of the ides of October’ or ‘the fifth ides of October’, meaning the fifth day (counting inclusively) before the ides of October, i.e. the 11th of October.

So, each month had an ides – and a nones and a calends – but the ides of March has been singled out for posterity, simply because of Shakespeare’s use of the words – and an inauspicious date for Julius Caesar.


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