... the ides of March

contrary to popular belief, this is not to be confused with superstitiously unlucky days like Friday the 13th's - however in the calendar in which "ides" originates there are 8 months whose "ides" fall on the 13th of the month, so if that occurs on a friday, it could be both the "ides" and unlucky. It was certainly an unlucky day for Caesar who should perhaps have been more discriminating in his choice of buddies.

the actual term "ides" purportedly comes from Romulus' (supposed founder of rome) first roman calendar. whichever twisted puppy invented this particular piece of work, he must not have had enough to do since trying to figure the date becomes a labrynthian task. each month revolves around 3 special days "Kalends, Nones, & Ides" each of which served as a reference point for counting the other days:

Kalends (1st day of the month)
Nones (the 7th day in march, may, july, and october; the 5th in the other months)
Ides (the 15th day in march, may, july, and october; the 13th in the other months)

the remaining, everyday days of the month were identified by counting backwards from the Kalends (origin of calendar - means account book and the first of the month id when bills came due even then), Nones, or the Ides. march 3 would be V Nones > 5 days before the Nones (the roman method of counting days was inclusive) in other words, the Nones would be counted as one of the 5 days.

apparently Romulus didn't like the latter half of any month, since all of the reference days appear between the first and the 15th. this system was also used in the Julian calendar (45 bce) and was in common use through the middle ages right up to the renaissance.

and if that isn't confusing enough, how about the egyptian calendar: the ancient egyptians used a calendar with 12 months of 30 days, for a total of 360 days/year. around 4000 B.C. they added 5 extra days at the end of the year to equate with the solar year. these five days became a festival because it was thought to be unlucky to work during that time.(still trying to find out the why of that one)

the egyptians had actually calculated that the solar year was actually closer to 3651/4 days, but instead of using a single leap year system, they let the 1/4 day accumulate. after 1,460 solar years, or four periods of 365 years, 1,461 egyptian years had passed. this means that as the years passed, the egyptian months fell out of sync with the seasons, so that the summer months eventually fell during winter. only once every 1,460 years did their calendar year coincide precisely with the solar year. but not to worry they had a separate religious calendar based on the lunar cycle, and christmas didn't exist yet :)