The Roman Calendar: From Romulus to Julius Caesar

Our months are Roman. Their names, their order and even their uneven lengths come from a calendar that grew up over more than seven centuries in the city of Rome. It was messy, political and full of superstition, and its final reform under Julius Caesar is the direct ancestor of the calendar on your wall.

Ten months and a missing winter

According to Roman tradition, the first calendar was created by Romulus, the legendary founder of the city. It had only ten months, starting in March, and covered just 304 days. The months were Martius, Aprilis, Maius, Iunius, Quintilis, Sextilis, September, October, November and December. The last six simply meant fifth, sixth, seventh, eighth, ninth and tenth.

What happened to the rest of the year? It seems the roughly sixty days of deep winter were simply not counted. There was little farming or warfare to organize, so the calendar paused until spring returned with the month of Mars.

Numa adds January and February

The second king of Rome, Numa Pompilius, is credited with adding two new months, Ianuarius and Februarius, to fill the winter gap. The year grew to 355 days. Romans considered even numbers unlucky, so most months were given an odd number of days. February, linked to purification and the dead, was left with an even number.

A 355-day year is about ten days too short, so the Romans needed to add an extra month from time to time. This month, called Mercedonius, was inserted after February when the priests decided it was needed.

A calendar run by politicians

Here is where things went wrong. The decision to add Mercedonius belonged to the pontiffs, the priestly officials who were often politicians too. A longer year kept friendly officials in power longer. A shorter one could cut an enemy's term. Wars and distractions meant the extra month was sometimes simply forgotten.

By the time of Julius Caesar the calendar had drifted badly. Festivals meant for harvest fell in other seasons, and the civil calendar was roughly three months out of step with the Sun.

Kalends, nones and ides

Romans did not number days from the start of the month as we do. Instead they counted backwards from three fixed points:

• The Kalends, the first day of the month, from which we get the word calendar.

• The Nones, on the 5th or 7th.

• The Ides, on the 13th or 15th, made famous by the Ides of March in 44 BC.

A date such as "the third day before the Ides" sounds odd today, but it was perfectly natural to a Roman. Romans also had an eight-day market cycle marked with the letters A to H, and you can see those letters running down the stone calendar on the cover of this post. It is part of the Fasti Praenestini, a marble calendar carved in the town of Praeneste around AD 6 to 10 and now in the National Roman Museum.

The year of confusion

In 46 BC Julius Caesar, advised by the astronomer Sosigenes of Alexandria, set out to fix the calendar once and for all. First he had to pull the dates back into line with the seasons. He did this by making 46 BC an extraordinary 445 days long, adding extra months so that the next year could begin in the right place. Romans called it the year of confusion.

From 45 BC the new Julian calendar took effect. It had 365 days, with the months lengthened to the familiar pattern we know today, and an extra day added every fourth year. In Rome the leap day was made by doubling the sixth day before the Kalends of March, which is why a leap year was once called bissextile.

Teething problems and new names

After Caesar's assassination the priests misunderstood the rule and added a leap day every three years instead of four. The emperor Augustus corrected the error by skipping leap years for a while until the calendar was back on track around AD 8.

Two months were renamed to honor the new rulers. Quintilis became July for Julius Caesar, and Sextilis became August for Augustus. The old numbered names of September to December remained, even though they were now the ninth to twelfth months, which is why the names no longer match their positions.

A long legacy

The Julian calendar was a huge success. It spread across the Roman Empire and remained the standard in Europe for more than 1,600 years. Its one flaw, a year about eleven minutes too long, would only be fixed in 1582. The next post in this series tells the story of that fix, and of the ten days that vanished from history.

Cover image: Fasti Praenestini, calendario con note prevalentemente dal 6 al 10 d.C. Palazzo Massimo alle Terme -FG2, CC0, via Wikimedia Commons.