European Calendar Traditions
22 entries from the European tradition: 4 calendar systems, 4 eras and year counts, 8 calendar reforms and adoptions, 4 calendar cycles and leap rules, 2 calendar-based observances.
Julian calendar
1 January 45 BCEJulius Caesar's calendar, designed mainly by the astronomer Sosigenes of Alexandria, took effect on 1 January 45 BCE. It has...
Revised Julian calendar
1923Proposed by the Serbian scientist Milutin Milanković and considered at a pan-Orthodox congress in Constantinople in May and June...
French Republican calendar
Decreed 24 October...Revolutionary France replaced the Gregorian calendar with twelve months of 30 days, each split into three ten-day décades, plus...
Roman Republican calendar
Before Caesar's reform the Roman year normally had 355 days, kept in step with the seasons by an intercalary month, Mercedonius...
Anno Domini
525 CEThe Anno Domini system was devised in 525 in Rome by the monk Dionysius Exiguus for his Easter tables, counting years from his...
Byzantine era
The Byzantine Empire dated years from creation, placed on 1 September 5509 BCE, with the year beginning in September. The count...
Ab urbe condita
Ab urbe condita, from the founding of the city, counts years from the traditional founding of Rome, which the scholar Varro...
Olympiad
Greek historians dated events by Olympiads, four-year periods beginning with the traditional first Olympic Games of 776 BCE...
Gregorian reform of 1582
24 February 1582...Pope Gregory XIII's bull Inter gravissimas, dated 24 February 1582, ordered that Thursday 4 October 1582 be followed by Friday 15...
Protestant German states and Denmark-Norway, 1700
1700Most Protestant states of the Holy Roman Empire, together with Denmark-Norway, switched in 1700 by following 18 February with 1...
Swedish calendar, 1700–1712
1700Sweden planned to reach the Gregorian calendar gradually by omitting every leap day from 1700 to 1740. It dropped the 1700 leap...
British calendar change of 1752
Calendar Act 1750...Under the Calendar (New Style) Act 1750, Great Britain and its colonies, including those in America, made Wednesday 2 September...
Bulgaria's calendar change, 1916
1916Bulgaria became the first Orthodox country to adopt the Gregorian calendar for civil use, following 31 March 1916 with 14 April...
Russia's calendar change, 1918
1918A decree signed by Lenin made Wednesday 31 January 1918 followed by Thursday 14 February. This is why the October Revolution of...
Greece's calendar change, 1923
1923Greece was the last European country to adopt the Gregorian calendar for civil use, following 15 February 1923 with 1 March. The...
Soviet work-week calendar
1929–1940From 1929 the Soviet Union replaced the seven-day week in workplaces with a continuous five-day week, the nepreryvka, with...
Metonic cycle
c. 432 BCE (Meton)The Athenian astronomer Meton observed that 19 solar years are almost exactly 235 lunar months, so moon phases recur on nearly...
Solar cycle (Julian)
In the Julian calendar the pattern of weekdays and dates repeats every 28 years, the product of the 7-day week and the 4-year...
Easter
Computus fixed after...Easter falls on the first Sunday after the ecclesiastical full moon on or after 21 March. In the Gregorian calendar Western...
Orthodox Christmas
Churches keeping the Julian calendar, including the Russian, Serbian and Georgian churches, celebrate Christmas on 25 December...
Octaeteris
6th century BCEThe earliest Greek intercalation rule inserted three leap months every eight years, since 99 lunar months nearly match eight...
Callippic cycle
330 BCECallippus of Cyzicus improved the Metonic cycle by taking four 19 year cycles, 76 years, and dropping one day, giving 940 months...