In the ancient Roman calendar, Ides was a day falling roughly in the middle of each month (the 15th day of March, May, July, and October, and the 13th of other months).
The Romans did not number each day of a month from the first to the last day. Instead, they counted back from three fixed points of the month: the Nones (the 5th or 7th, nine days inclusive before the Ides), the Ides (the 13th for most months, but the 15th in March, May, July, and October), and the Kalends (1st of the following month). Originally the Ides were supposed to be determined by the full moon, reflecting the lunar origin of the Roman calendar. In the earliest calendar, the Ides of March would have been the first full moon of the new year.
Most notably associated with the assassination of Roman Emperor Julius Ceasar by his Senate in 44 B.C., the Ides of March has the reputation of being unlucky.
The Ides were the designated days for settling debt each month in the Roman empire and generally included the seven days preceding the Ides for this purpose. No doubt debtors who could not pay their debts considered the Ides to be unlucky days as they were typically thrown into prison or forced into slavery.
The Ides of each month were sacred to Jupiter, the Romans’ supreme deity. Jupiter’s high priest, led an “Ides sheep” in procession along the main street of ancient Rome to the citadel, where it was sacrificed.
In addition to the monthly sacrifice, the Ides of March was also the occasion of the Feast of Anna Perenna, a goddess of the year whose festival originally concluded the ceremonies of the new year. The day was enthusiastically celebrated among the common people with picnics, drinking, and revelry. Celebrate the Ides with a bit of revelry of your own.