The Roman calendar or fasti began as a seasonal calendar but developed into a register of days for legal or public business. It is believed to have been introduced to Rome from Etruria sometime before the fall of the Roman Kings. This supposition is based on the root of some month names, such as “June”, derived from uni, the Etruscan spelling for the goddess Juno.

The calendar underwent a significant revision during the dictatorship of Julius Caesar, who introduced the concept of the leap year, forming the basis for the modern western calendar.

A Lunar Calendar

The original Roman calendar followed the seasons and was essentially lunar based. Each month had special named days that corresponded to different moon phases. These were the calends, nones and ides.

The calendar became a ten-month, solar-orientated calendar briefly during the rule of Romulus, with the year running from March to December, leaving the winter months uncounted. It reverted to twelve months under the second king of Rome, Numa Pompilius.

The Julian Calendar

By the republic, the calendar was organised to suit the political year. Important historical dates were recorded not by the year but by the name of the consul in power at the time.

The year itself was 355 days long. March, June, July and October were each 31 days long, and all the rest were 29 days apart from February, which only amounted to 23 or 24 days. In between was an intercalary month of around ten days designed to align the months with the electoral calendar.

As a result, the calendar fell out of line with the natural year, running three months ahead of the solar year by the time of Julius Caesar. So Caesar decided to reform the calendar to realign it with the seasons and used the Egyptian solar calendar as the basis. The year 46BC was lengthened to 445 days to bring it back into line and the new calendar was implemented on the first day of 45BC.

This new calendar was based on a 365-day year, with the extra ten days added to the shorter 29-day months. Rather than adding a whole intercalary month each year, Caesar introduced the practice of adding one day between the 23rd and 24th of February every fourth year. This meant that the 23rd occurred twice during what became known as the leap year.

The Calendars of Augustus, Tiberius and Pope Gregory the Thirteenth

Julius Caesar’s death saw the calendar again becoming subject to miscalculations until it was brought back into line by his heir, the emperor Augustus. He and the emperor Tiberius made minor changes to create what we know as the modern western calendar of today. The Julian calendar remained in place in the same essential form until 1582, when it was re-organised again by Pope Gregory the thirteenth into what became known as the Gregorian calendar.

Resources:

Boyle, A J and Woodward, R D (trans and edited) (2000) Ovid’s Fasti. Penguin Books: London.

The Oxford Classical Dictionary.