The Roman Calendar

The 'Mercurius' inscription refers to the Ides of February. Most of us have heard of the Ides of March from Shakespeare's "Julius Caesar", when the seer tells Caesar to beware the Ides of March.  But what were the Ides? and how did the Romans tell what day it was?

First off, we inherited our months from the the Romans, so the names of the months are the same as theirs, even down to the clue that the first month of the year was not January (Septem, Octo, Novem, Decem). The Romans did not use weeks, however, but referred to three days in each month by name:  the Ides, the Nones, and the Kalends.  The Kalends (from which we get 'calendar') was the first day of the month; the Nones was the 7th, and the Ides the 13th.  Ah ha!, you say, but the Ides of March is March 15th!  That's true; for March, May, July, and October, the Nones fell on the 9th and the Ides on the 15th.  These three days were used for market days, interest calculations, and legal proceedings.

The strangest thing about the Roman calendar to modern eyes, though, is how they counted the days.  We count forward from the first day of the month; e.g., the 2nd of December, the 25th of May, etc.  The Romans counted forward to the next named day of the calendar. So , for example, since May 10th is six days before May 15th (counting both the beginning and ending date, which they did), them May 10th was known as the 6th day before the Ides of May.  Today, November 16 in modern reckoning, is the 16th day before the Kalends of December.

This calendar had developed in the very first days under the Etruscans, when Rome was still a country village, and so the reason for counting like this was that, as an agrarian society, they had no need to know how many days had passed since the last market day;  they did, however, have a vital interest in knowing when they had to get their produce to the forum for the next market day.

http://en.wikipedia.org/wiki/Roman_calendar