The Ides of March?

In the ancient Roman calendar, each of the 12 months had an "ides." In March, May, July and October, the ides fell on the 15th day. In every other month, the ides fell on the 13th. The word "ides" was derived from the Latin "to divide." The ides were originally meant to mark the full moon - but since the solar calendar months and lunar months were of different lengths, the ides quickly lost their original intent and purpose.