Happy Leap Year!

Written By Kari Campbell

Since 45 B.C., leap years have been used to reconcile calendars with the actual time it takes for the earth to circle the sun. It takes the earth 365 days, 5 hours, 48 minutes and 45 seconds to revolve around the sun, not 365 days. If left uncorrected, calendar dates and important events, such as the vernal and autumnal equinoxes and the solstices, will slowly shift until they don’t match their prescribed calendar dates [March 21 (Vernal equinox), September 23 (Autumnal equinox); June 21(Summer Solstice) and Dec 22 (Winter Solstice)].

After a century, our calendar would be off by about 24 days.

The Hebrew, Chinese and Buddhists have used different methods to reconcile the earth’s orbit with their calendars, and so has Western civilization. Our efforts to sync the calendar with the earth’s revolution around the sun dates back to the time of Julius Caesar.

Gaius Julius Caesar - Surveyor of the Appian Way

The Tusculum portrait, possibly the only surviving sculpture of Caesar made during his lifetime.

Gaius Julius Caesar (100-44 BCE), was a military genius who vastly extended the boundaries of the Roman Republic across Europe—all the way to the Atlantic Ocean and English Channel while he was governor of Gaul.

He was also a savvy politician and “eloquent speaker who was even able to turn personal tragedies into political gains. When his first wife, Cornelia, died in 69 B.C., Caesar used her funeral to grow his support by breaking with tradition and giving an oration that appealed to the people and showcased his caring side.” [1]

Whenever Caesar was appointed to a new position, he lavishly spent his own money (often borrowed from wealthy backers) on public structures, games and other popular projects, which then helped him get elected or named to another, more influential office. One of these offices was Surveyor or Curator of the Appian Way, which he took over in 67 BCE. The Surveyor’s office was of the praetorian rank, only a few levels down from emperor, so Caesar was working his way up. There’s no information that Caesar actually surveyed anything himself, but he is credited with upgrading and expanding the road.

The Appian Way

Keystone View Company, P. Original paving on the Appian way, Rome, Italy. Italy, None. [Between 1860 and 1930] [Photograph] Retrieved from the Library of Congress.

Begun back in 312 BCE, the Via Appia was a strategically important road that connected Rome with Brindisi, a port on Italy’s southeast coast. It was key to Rome’s conquest of southern Italy, and later, to its conquests across the Mediterranean. By the time Ceasar was in charge, the road needed extensive upgrades and expansions, which he oversaw. He lavished great care and expenditure on its renovation.[2] The surveying and engineering work on the road used many revolutionary techniques, one of them being a new form of concrete called “opus caementicium,” that created a durable and stable surface. The road’s construction required advanced engineering techniques to traverse difficult terrains using viaducts and bridges.

In Caesar’s platform as Surveyor or Curator of the Appian Way, he began to push for extensive reforms of Roman society and government. He proposed a law for the redistribution of public lands to the poor and made plans for the distribution of land to his veterans, including the establishment of veteran colonies throughout the Roman world. He planned, but did not complete, a land survey of the entire empire.

The Julian calendar and the first leap year

One of Julius Caesar’s enduring legacies is the Julian calendar. Soon after he became dictator in 45 BCE, he decided that the calendar had to be reformed.

A reproduction of the Fasti Antiates Maiores, a painted wall-calendar from the late Roman Republic.

“Introduced around the seventh century B.C., the Roman calendar attempted to follow the lunar cycle but frequently fell out of phase with the seasons and had to be corrected. In addition, the pontifices, the Roman body charged with overseeing the calendar, often abused its authority by adding days to extend political terms or interfere with elections.”[3]

To create the new calendar, Caesar was assisted by Sosigenes, an Alexandrian astronomer. Sosigenes advised him to follow the solar year instead of the lunar year. Based on the sun, the year was calculated to be 365 and 1/4 days, and Caesar added 67 days to 46 B.C., making 45 B.C. begin on January 1, rather than in March. He also decreed that every four years a day be added to February, thus theoretically keeping his calendar from falling out of step.

A bit out of sync

Lunario Novo, Secondo la Nuova Riforma della Correttione del l'Anno Riformato da N.S. Gregorio XIII, printed in Rome by Vincenzo Accolti in 1582, one of the first printed editions of the new calendar.

Things went along really well until the mid-16th century when astronomers noticed that the seasons were beginning around 10 days earlier than expected when important holidays, such as Easter, no longer matched up with specific events, such as the vernal equinox.

By that time, the popes were in charge of the Holy Roman Empire, and Pope Gregory XIII tweaked the Julian Calendar by removing the leap year for most centenary years. He also renamed it after himself, so the calendar now used in most of the world is the Gregorian Calendar. Some Eastern Orthodox churches still use the Julian calendar to determine liturgical dates, such as the date for Easter.

Back in sync

It’s amazing to think that more than two millennia after leap year was originally instituted by Caesar (and tweaked by Pope Gregory), leap year is still used to make sure our calendars are in sync with the earth circuit around the sun.

Today, because 2024 isn’t the start of a century, we all enjoy an extra 24 hours to make sure our Gregorian calendar matches the revolution of the earth around the sun. Precision is important for calendars - and for surveying, as Julius Caesar knew back in 67 BCE. Surveying was essential back then, and they even had a god, Terminus, whose feast is celebrated in February: Terminalia. Happy leap year and happy Terminalia!

Kari Campbell
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