Julius Caesar's bloody assassination on March 15, 44 B.C., forever marked March 15, or the Ides of March, as a day of infamy.
For ancient Romans living before that event, however, an ides was merely one of several common calendar terms used to mark monthly lunar events. The ides simply marked the appearance of the full moon.
During the time of ancient Rome, each month began with the calends, from the Latin term meaning "proclaim" or "call." The term referred to the announcement of the first sighting of the new moon and was also associated with the day interest was due.
Following the calends came the nones, which marked the first quarter moon. Its meaning ("nine") was derived from the term for the Roman nine-day week, nundinae. One nundinae after the nones came the ides. The term, which means "to divide," designated the occurrence of the full moon.
The ancient Roman calendar fixed the calends on the 1st, the nones on the 5th or the 7th, and the ides on 13th or the 15th. The months of March, May, July, and October, the longest months at 31 days, held the nones on the 7th and the ides on the 15th. For all other months the nones fell on the 5th and the ides on the 13th.
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