(15 March) The Ides of March is a day on the Roman calendar that is March 15. It became notorious as the date of the assassination of Julius Caesar in 44 BC. The Romans counted back from three fixed points of the month: the Nones (5th or 7th), the Ides (13th or 15th), & the Kalends (1st) of the following month. The Ides were supposed to be determined by the full moon, reflecting the lunar origin of the calendar. On the Roman calendar, the Ides of March is the first full moon of the new year.