Simply, the Romans followed this monthly cycle:
· Kalends = day 1
· Before the Nones = days 2 – 6
· Nones = day 7 – which signified the first quarter of the moon
· Before the Ides = days 8 – 14
· Ides = day 15 - originally the full moon
· Before the Kalends = days 16 – 30 / 31 [ie before the next month]
Originally the Ides of March once signified the new year, which meant celebrations and rejoicing, however it became synonymous with doom and gloom courtesy of William Shakespeare. In the play Julius Caesar the dictator was warned by a soothsayer “Beware the Ides of March” and the following scenes played out the events of 44BC when Caesar was assassinated by 60 senators led by Brutus and Cassius.
So - there you go!