Most of the world’s countries and cultures use the Gregorian calendar, but some base their calendars on more ancient systems. Other countries have adopted an alternative calendar at some point in their history. 3761 BC Jewish calendar starts 2637 BC Original chinese calendar starts 45 BC Julian calendar adopted by Roman Empire AD 1 Christian calendar starts 79 Hindu calendar starts 597 Julian calendar adopted in Britain 622 Islamic calendar starts 1582 Gregorian calendar introduced in Catholic countries 1752 Julian calendar abandoned, Gregorian calendar adopted in Britain and its colonies, including America 1873 Japan adopts the Gregorian calendar 1949 China adopts the Gregorian calendar