Ides of March
The Ides of March has long been considered an ill-fated day. Julius Caesar was assassinated on March 15, 44 B.C. Historians note that it is likely that a soothsayer named Spurinna had warned Caesar that danger would occur by the ides of March. William Shakespeare included the phrase "Beware the ides of March" in his play Julius Caesar.
The ides were the 15th days of four months (Martius, or March; Maius, or May; Quintilis, or July; and October) in the ancient Roman lunar calendar; they were the 13th in all other months (originally, Aprilis, or April; Iunius, or June; Sextilis, or August; September; November; and December. Ianuarius, or January, and Februarius, or February, were added later).
The word ides comes from the Latin word idus, which is possibly derived from an Etruscan word meaning "to divide." The ides were originally meant to mark the full Moon (the "halfway point" of a lunar month), but because the Roman calendar months and actual lunar months were of different lengths, they quickly got out of step. The ancient Romans considered the day after the calends (first of the month), nones (ninth day before the ides, inclusive), or ides of any month as unfavorable. These were called dies atri.