<P> Dionysius Exiguus, and others following him, maintained that the 318 Bishops assembled at the Nicene Council had specified a particular method of determining the date of Easter; subsequent scholarship has refuted this tradition . In any case, in the years following the council, the computational system that was worked out by the church of Alexandria came to be normative . It took a while for the Alexandrian rules to be adopted throughout Christian Europe, however . The 8 - year cycle originally employed was replaced by (or by the time of) Augustalis's treatise on the measurement of Easter, after which Rome used his 84 - year lunisolar calendar cycle until 457 . It then switched to an adaptation by Victorius of the Alexandrian rules . </P> <P> Because this Victorian cycle differed from the Alexandrian cycle in the dates of some of the Paschal Full Moons, and because it tried to respect the Roman custom of fixing Easter to the Sunday in the week of the 16th to the 22nd of the lunar month (rather than the 15th to the 21st as at Alexandria), by providing alternative "Latin" and "Greek" dates in some years, occasional differences in the date of Easter as fixed by Alexandrian rules continued . The Alexandrian rules were adopted in the West following the tables of Dionysius Exiguus in 525 . From this time, therefore, all discrepancies between Alexandria and Rome as to the correct date for Easter cease, as both churches were using identical tables . </P> <P> Early Christians in Britain and Ireland also used an 84 - year cycle . From the 5th century onward this cycle set its equinox to 25 March and fixed Easter to the Sunday falling in the 14th to the 20th of the lunar month inclusive . This 84 - year cycle was replaced by the Alexandrian method in the course of the 7th and 8th centuries . Churches in western continental Europe used a late Roman method until the late 8th century during the reign of Charlemagne, when they finally adopted the Alexandrian method . Since 1582, when the Catholic Church adopted the Gregorian calendar while the Eastern Orthodox and most Oriental Orthodox Churches retained the Julian calendar, the date on which Easter is celebrated has again differed . </P> <P> The Greek island of Syros, whose population is divided almost equally between Catholics and Orthodox, is one of the few places where the two Churches share a common date for Easter, with the Catholics accepting the Orthodox date--a practice helping considerably in maintaining good relations between the two communities . </P>

Where did the easter holiday originated from and why is it celebrated