March 15th is know as the Ides of March and made famous by Julies Caesar…
I. The Ides of months (the 15th day in March, May, July, and October; the 13th in the other months), marked important deadlines in the Roman calendar. The Ides of March was used traditionally to manage and settle financial debts[2]. This likely stems from the fact the Ides of March was in the original (pre-Julian) Roman calendar the first Ides of the year, bringing the previous year to an official end.
II. It was William Shakespeare that popularised the phrase ‘beware the Ides of March’, where it’s presence in his play Julius Caesar was an embellished dramatisation of conversations between Caesar and a soothsayer. According to Plutarch[3], a soothsayer warned Caesar, prior to the Ides of March, of the events to come. Caesar then again saw the soothsayer the morning of his assassination who repeated the warning, but Caesar dismissed it, confident in his popularity with the people and Senatorial class of Rome.
III. Until Christianity became the official religion of the Roman state, all Ides’ were sacred to Jupiter. The Ides’ were celebrated with the Flamen Dialis (high priest of Jupiter) leading the ovis Idulius (Ides sheep) along the Via Sacra in Rome to the ancient citadel on the Capitoline hill (arx) to be sacrificed every month[4]. This sacrifice typically commenced a festival or major occasion, and in the case of the Ides of March it marked the beginning of the Feast of Anna Perenna, goddess of the year and concluded the ceremonies of the Roman new year.[5]
IV. Julius Caesar’s assassination aside, the Ides of March has also marked the date of other major events in history[6], including Christopher Columbus’ return to Spain after his first journey to the New World (1493), Woodrow Wilson holding the first US presidential press conference (1913) and the abdication of Tsar Nicholas II of Russia (1917).
https://www.romanculture.org/journal/2018/3/14/be-aware-of-the-ides-of-march-4-things-to-know-about-the-infamous-day