Britannica: "The Council of Nicaea in 325 decreed that Easter should be observed on the first Sunday following the first full moon after the spring equinox (March 21). Easter, therefore, can fall on any Sunday between March 22 and April 25."
The correct date for Easter was a huge deal in the early Church. The Pope brought Easter back into conformity with Nicaea by reforming the calendar -- astronomical knowledge had improved a lot over the centuries.
The correct date for Easter was a huge deal in the early Church. The Pope brought Easter back into conformity with Nicaea by reforming the calendar -- astronomical knowledge had improved a lot over the centuries.