This week is significant, for religious reasons it has not always existed.

It was in 1582, Pope Gregory XIII instituted a major reform of the calendar, which has since been almost universally adopted.  But that year, the time period of October 5 to 14 was removed from the calendar, making October 4 followed by the 15th of the month. This week is back again and is unlikely to be removed again.

Pope Gregory was concerned because the calendar was slowly moving the day of Easter further and further away from the Vernal Equinox. The problem emerged 16 centuries earlier.

Originally the calendar used by the ancient Romans was one attributed to ancient Roman Kinga Romulus and Numa. Romulus is said to have created a new calendar for the founding of Rome, which consisted of 10 months. His successor King Numa reorganized to 12. It has a number of eccentricities, including that it had to be revised each year by a body of priests called the College of Pontiffs. They would sacrifice animals and through augury, or the reading of entrails, determined which pagan holy days fell on which date. The old calendar was not based on the sun, but on the moon and the agricultural seasons. Their longest year lasted for 444 days and new year’s day was often around March.

All of this confusion came to an end in 45 B.C.

The dictator Julius Caesar had won a major civil war, and invoking his powers as high priest of the Roman Republic issued a new calendar, later known as the Julian Calendar. This kind of calendar was based on the number of days it took for Earth to go around the sun, 365 and a quarter days. Caesar had spent a considerable amount of time campaigning in Egypt, where the highest god was Amun-Re, the sun god, and his worship was what determined the Egyptian Calendar. Basing the year on 365.25 days per year seemed a much more accurate way of keeping astronomy and the marking of time in sync, and Caesar even adopted the leap year to keep it accurate. We may thank the Queen of Egypt, Cleopatra VII for her influence on Caesar. This calendar remained in place until Pope Gregory XIII.

But Caesar did not know that the rotation of Earth was in point of fact not 365.25 days but 365 days, 5 hours, 48 minutes, and 46 seconds long. This was a small amount of time to forget about but over the centuries the date of the Spring Equinox slowly drifted away from the new year. The intellect behind this discovery was that of the German born Jesuit priest, Fr. Christopher Clavius SJ, who advised Pope Gregory of the situation and advocated a solution. Clavius’ name was immortalized by the naming of the largest lunar crater after him.

Gregory XIII was a great reformer, who reduced the power of the cardinals and assumed more power to himself. He supported the decrees of the Council of Trent, and advocated for the revised Breviary and the religious holy days in the revised Roman calendar. He issued the Papal Bull Inter gravissimas in 1581, which set out the reforms to the calendar. He enjoined all to establish it, thoughtfully adding “It is therefore entirely forbidden to any man to infringe these our precepts and decrees, mandates, statutes, will, approval, prohibition, sublation, abolition, exhortation and request, or to dare to bear witness or proceed against them. If nevertheless any presume to make such an attempt, they are to know that they will incur the indignation of almighty God and of the blessed apostles Peter and Paul.” Ouch.

The reforms to the calendar were soon adopted by the Catholic nations of Europe, but the Protestant and Eastern Orthodox were a little suspicious. There were actually riots in London by outraged people who thought Pope Gregory was trying to deprive them of 10 days of their lives. But Father Clavius’ equations were hard to argue with and slowly over the centuries most of the European nations adopted the calendar. Great Britain and her colonies adopted the Gregorian Calendar in 1752. The last European state to adopt it was Greece in 1923. The Eastern Orthodox Churches still use the Julian Calendar for their liturgical use.

One of the less well-known aspects of the Gregorian reform is that January 1 was decreed to be New Year’s Day. Before Gregory XIII the new year was based on different days in various countries, such as Dec. 25, March 1, the moveable date of Easter and very commonly April 1. Those who continued the use dates other than Jan. 1, were ridiculed and called an “April Fool.”

Gregory Elder, a Redlands resident, is a professor emeritus of history and humanities at Moreno Valley College and a Roman Catholic priest.

Write to him at Professing Faith, P.O. Box 8102, Redlands, CA 92375-1302, email him at [email protected] or follow him on Twitter @Fatherelder.