Between AD326 and AD1582, Christianity determined Easter using an algorithm approved by a Church Council in AD325, with the equinox defined as March 21.
From AD1054 (when the Orthodox and Catholic Churches split) through AD1582 both the Catholic and Orthodox Churches celebrated Easter on the same date, still using the algorithm from AD325.
Days before Easter Days after Easter Triodon 70 Ascension 39 Sat.
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D.), one finds that, in fact, Easter occurred on the first day of Passover several times before the year A. (I've compiled some Tables showing the offsets between Orthodox and Western Easters from 1583 through 3000 that shows this information.) In the 1923 May there was a well documented meeting that provided for Calendar Reform in of the Orthodox Church.