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A new calendar system, introduced in 1582, was named the Gregorian calendar in honor of Pope Gregory XIII, who initiated the calendar transition. Gregorian calendar approaches the tropical year much closer than its predecessor - Julian calendar, see Julian and Gregorian calendars. The calculator below converts a Julian date to the Gregorian date for the common era dates.
The common era is a contemporary starting point for years numbering worldwide. In the past, different countries chose different calendar eras for the chronology. Sometimes, there were several eras in use simultaneously in a single country. Therefore, to interpret a historical date correctly, you should clarify which era is this date belongs to. The following calculator converts a Julian date to the Gregorian date, taking into account the era.
Roman Empire started to number years from 1, whenever a new ruler comes to power. Diocletian era (years started from Roman Emperor Diocletian reign in 284 CE) was very popular for a few centuries until the adoption of Common Era (Anno Domini) in Western Europe countries.
Anno Domini era becomes one of many chronology starting points in the VI century thanks to Dionysius Exiguus, Rome monk, who calculated the easter tables in 525 CE. Dionysius did not want to number years from Rome Emperor Diocletian's reign (the most common era in those times). Instead, he introduced a Christ birthday year as Year One of the new Anno Domini era. Two centuries later, the Anno Domini era became dominant in Western Europe.
Eastern Europe, influenced by the Patriarchate of Constantinople, went their own way: years numbering started since creation of the world (Annus Mundi). According to this era the Year One started on September 1st, 5509 (or earlier on Match 1st 5508). In Russia, this year numbering system existed till 1700. This year Tzar Peter ordered to use Julian's calendar in conjunction with the Anno Domini era and January 1st as the first day. See Old Russian (Byzantine) system of chronology for more details.
Iberian peninsula countries used their own era (Spanish era) before the domination of the common era. Spanish era Year One corresponds to 38 B.C. The Christian era gradually replaced the Spanish era during the 12-16 centuries.
The calculator uses the era starting year and day for date conversion. Information about the eras exploited by the calculator was collected in the Calendar Era directory. Edits and corrections of the directory are welcome.