Beware the Ides of March!

The Romans had special names for three specific days in each month. Origianlly the system appears to have been based on phases of the Moon (Luna). In the early days of the Republic they became fixed days.

The named days were:

• Kalendae (Kalends) — first day of the month, from which the word "calendar" is derived; thought to have originally been the day of the new moon. Interest on debt was due on Kalends (Oi!).
• Nones — depending on the month, could be the 5th or the 7th day; originally thought to have been the day of the half moon.
• Ides — depending on the month, could be the 13th or the 15th day; thought to have originally been the day of the full moon. The Romans considered this an auspicious day in their calendar.

Months with Nones on the 5th and Ides on the 13th days: January, February, April, June, August, September, November, December.

Months with Nones on the 7th and Ides on the 15th days: March, May, July, October.

These rules are summarised in the following mnemonic:

In March, July, October, May

The Ides fall on the fifteenth day

The Nones the seventh; all besides

Have two days less for Nones and Ides.

Thus endith the lesson...