The Roman calendar was based on a lunar cycle and was created by Romulus, the first king of Rome. The calendar began in March and the first full moon of the year was on March 15th. This would become a period of celebration in Roman culture. The Romans would leave the city and gather at the Tiber River to celebrate with food and drink for a period of three days. It was a new year festival of sorts for the Romans. March 15th also had political significance as it marked the day when two new consuls would begin to govern Rome.

Julius Caesar was appointed dictator for life, effectively marking the end of the Republic period of Roman history. Caesar revised the calendar in 46 BC which moved the new year to January. As fate would have it, Julius Caesar was murdered by a group of senators on March 15th of 44 BC and he is forever linked with the Ides of March. William Shakespeare, in his play Julius Caesar, immortalized the story of a warning given to Julius Caesar with the line "beware the Ides of March." The Roman biographer Suetonius identifies the person that warned Caesar as a soothsayer named Spurinna.