The Roman calendar was reformed by Julius Caesar in 45 BC.The Julian calendar was no longer dependent on the observation of the new moon but simply followed an algorithm of introducing a leap day every four years.Toraen leses som en kronologisk forklaring fra israelittenes tidlige historie og hvordan Gud har kommet inn i historien for å enten straffe eller hjelpe det jødiske folk. En noe ulik versjon av toraen utgjør samaritanenes hellige skrift.
A large number of calendar systems which were based on the Babylonian calendar, and which were found in the Ancient Near East, date from the Iron Age.
A calendar can also mean a list of planned events, such as a court calendar or a partly or fully chronological list of documents, such as a calendar of wills.
Periods in a calendar (such as years and months) are usually, though not necessarily, synchronised with the cycle of the sun or the moon.
This resulted in an observation-based lunar calendar that shifts relative to the seasons of the solar year.
The first calendar reform of the early modern era was the Gregorian calendar, introduced in 1582 based on the observation of a long-term shift between the Julian calendar and the solar year.