How was the calendar created?

Key dates for the calendar history

Around 4000 BC

The water of the Nile is the inspiration for the first calendar development of the Egyptians. Due to its regular flooding, the river brings the farmers fertile soil once a year. The floods are repeated approximately every 365 days.

For this reason, the Egyptians define three seasons from an agricultural point of view: flooding, sowing and harvest. The most important date is the first seasonal appearance of the star Sirius, which coincides closely with the beginning of the Nile flood. Presumably this date is also the ancient Egyptian New Year's Day.

Around 3000 BC

The Sumerians in Mesopotamia were the first to develop a calendar in the so-called sexagesimal system. That means: a day has 24 hours, an hour has 60 minutes and a minute has 60 seconds.

Around 2000 BC

The Babylonians in Mesopotamia develop a calendar that relates to the course of the moon around the earth. You calculate a little more than 29.5 days for this orbital period. Therefore, twelve months of 30 days each are combined into one year.

However, since the length of a solar year is almost 365.25 days, add a 13th leap month as required.

753 BC

The beginning of the Roman era: The Roman scholar Marcus Terentius Varro (116-27 BC) established the foundation of the city of Rome for this fictional year.

Around 700 BC

As the first king of Rome, Romulus had introduced ten Roman months. Now the legendary second king Numa Pompilius (750-671 BC) adds two more months to the calendar: Januaryis and Februaryis.

Around 528 BC

The Persians are the first to introduce a regular 13th leap month, which is inserted every 19 years.

432 BC

The astronomer Meton is developing a new calendar cycle in Greece. In a complicated procedure, it calculates the least common multiple of the orbit of the earth and the moon.

By properly setting the number of days in the year on a calendar that takes into account the moon and sun, this cycle works relatively accurately and only needs to be corrected by one day every 228 years.

The metonic cycle is only replaced by the introduction of the Julian calendar. Even today it is used to calculate the Christian Easter festival.

153 BC

The Roman Senate is moving the beginning of the year from March 1st to January 1st. The so-called counting months September (from the Latin "septem" = seven), October (from the Latin "octo" = eight), November (from the Latin "novem" = nine) and December (from the Latin "decem" = ten) move two positions further forward, but have kept their original names to this day.

Around 45 BC

The introduction of the Julian calendar: Gaius Julius Caesar put an end to the inaccuracies of the existing calendar with a reform. The Greek astronomer Sosigenes from Alexandria is developing a new system for this.

A normal year with 365 days is introduced; new rules for leap years are determined with the aim of fixing the vernal equinox as much as possible on a fixed date on the calendar.


At the first ecumenical council in Nicaea, the beginning of spring is set for March 21st. Further resolutions of the council: Determination of the date of Easter on the first Sunday after the first full moon after the beginning of spring and introduction of the seven-day Judeo-Christian week.


The monk Dionysius Exiguus introduces the calendar "Anni ab incarnatione Domini", which is later changed to "Anno Domini (" in the year of the Lord ").

The beginning of the new era is the fictional date of the birth of Jesus Christ and no longer the assumption of office of the Roman emperor Diocletian (September 29, 284). This type of time calculation gradually established itself in the Middle Ages and is now the most common worldwide.


Pope Gregory XIII decrees a calendar reform. It is named after him and ensures that the irregularities of the Julian calendar are evened out.

Because the Julian calendar is too long and ten additional days have accumulated since the Council of Nicaea, further switching rules are introduced. The superfluous days are simply deleted from the calendar. October 4, 1582 is thus directly followed by October 15, 1582.

The Gregorian calendar was not adopted by many Protestant countries until the 18th century, in Russia not until 1918 and in Turkey even not until 1927.


A revolutionary calendar based on the decimal system is introduced in France. The departure from the previous social order should also be reflected in the calendar system.

The year is divided into twelve months of 30 days each. At the end of the year, five or six days are added, which are considered holidays. A month consists of three decades of ten days each, the day of ten hours, the hour of ten other parts, and so on.

But the calendar did not take hold for long: the Gregorian calendar was reintroduced as early as 1806 under Napoleon.


In Germany, a new standard is being implemented to define the calendar weeks. As of January 1, 1976, the week starts on Monday. The first calendar week of the year is the week that includes at least four of the first seven days of January.