The History of the Western Calendar

by Niclas Marie

Old egyptian calendar in the Karnak temple.

In the earliest times, human beings calculated time by observing the periods of light and darkness that alternated continuously. The solar day is considered the earliest form of the calendar. The second basic type of calendar was the arbitrary calendar, which was created by counting the number of days over and over again, either towards infinity or in a cycle. Nonetheless, there were several problems with the arbitrary calendar. Firstly, farmers of early civilizations could not calculate the perfect time to plant their crops. Crop planting is an activity that is closely linked to the seasons, and the arbitrary calendar was not based on the durations of seasons. Therefore, humans began to observe the sun’s passage through a fixed point, and this practice was the precursor of the solar calendar. Calendars that were based on lunar and stellar cycles were also used in the ancient times.

Earlier Historical Calendars

One of the first truly scientific calendars was the Egyptian calendar. According to this calendar, a year comprised of 12 months, and each month had exactly 30 days. The months were further divided into three weeks, with each week lasting 10 days. Later on, the Babylonian calendar was developed, and it was a lunisolar calendar. The years in this calendar were made up of 12 lunar months, and each month would begin when a new crescent moon appeared. The Greeks used a calendar that was very similar to the Babylonian calendar, but they also had other calendars, such as the democratic state calendar with 10 arbitrary months and an agricultural calendar. The first Roman calendar was created by Romulus, and it had 10 months in a year, with each month lasting 30 or 31 days. The Romans had a number of calendars, and the most notable one was the Julian calendar. The Jewish calendar was another early type of calendar, and it contained no epagomenal days. The seventh day was called Sabbath.

The Julian Calendar

The Julian calendar was introduced in 45 BC by Julius Caesar. Although it had 12 months, many of its months were shorter than the months in the modern calendar. As such, one Julian year only consisted of 355 days. Before Julius Caesar’s reforms, the year began on the 31st of March. A leap month with 23 or 24 days was also created to keep the calendar properly aligned with the cycle of seasons. The Roman calendar also had a recurring cycle of weeks that is similar to the modern cycle, but each week comprised of eight days. Julius Caesar brought in a number of reforms to the old Roman calendar. One of them was the addition of days to February to make it a 28-day month. The week was also reduced by one day to make it a 7-day week. Additionally, Caesar introduced the leap year rule, which stated that all leap years can be evenly divided by four.

The Calculation of Easter

In his seminal work Ecclesiastical History of the English, the historian Bede described how the Roman Church and Irish Church had divided opinions on the calculation of Easter. At the synod of Wilby, King Oswy heard both sides of the argument and finally decided to vote for the Roman method, which suggested that Easter Day should fall on the first Sunday after the paschal full moon. The influence of the powerful Roman Church of the 14th century also ensured that most European regions adopted the Roman calculation. It was during this time that the “Anno Domini” dating, or “AD”, was implemented. Anno Domini is the counting of years from the time of Jesus Christ’s incarnation.

The Gregorian Conversion

In the year 1582, Pope Gregory XIII decreed that there should be a change in the Julian calendar. The Gregorian calendar was a theoretical calendar, and it was created from very precise calculations of vernal equinoxes. The Julian calendar was based on the assumption that the duration between vernal equinoxes is 365 ¼ days, but in reality, it is approximate ly 11 minutes less. As such, the Gregorian calendar had three leap days removed every four hundred years. Also, changes were made to the lunar cycle, which helped in the calculation of Easter. Many European countries did not adopt the Gregorian calendar when it was introduced, mainly because of the Protestant Reformation that was taking place at that time. Nevertheless, by the 20th century, the calendar became the standard calendar in Europe. Today, it is the most widely used calendar in the world. 

For more information on the history of western calendar, visit the following sites: 



About the author

is the founder and CEO of TimeCenter Online Scheduling and lives in Helsingborg, Sweden. He loves to code beautiful and simple web apps, and occasionally enjoys a game of blitz chess.






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