ROMAN NONES AND IDES
The Roman calender used "reverse-count" dates, each date being termed as so many days before the Calends, then the Nones, then the Ides of a month.
The start of a month was known as the CALENDS and mid-month the IDES (or "division"), meant to coincide with full moon. The 2nd of Ides of a month was one day before the Ides of a month, and the NONES (Lat."nonus", ninth of) was the eighth day before (or ninth day before-&-including) the Ides. For a mnemonic of their forward-dates for certain months:
March, July, October, May
In all other (longer) months they were set 2 days earlier (ie. on the 5th and 13th). The reason for being two days (rather than one) earlier was to avoid the 6th and 14th, because even-numbered days (such as the 14th) were regarded as unlucky for religious festivals, and therefore avoided as much as possible!
Here's another mnemonic rhyme on the subject, written by E. Cobham Brewer:
On March the 7th, May, July,
Julius Caesar (born c.102 B.C.) was assassinated in the Senate at Rome on the Ides (ie. the 15th) of March in 44 B.C., as forewarned by many of his friends and enemies alike, for planning to turn Rome from a Republic into a Kingdom. Some 17 years later, Rome established an Empire under the first of its five Caesarean Emperors.
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