Easter letter

The Festal Letters or Easter Letters are a series of annual letters by which the Bishops of Alexandria, in conformity with a decision of the First Council of Nicaea, announced the date on which Easter was to be celebrated. The council chose Alexandria because of its famous school of astronomy, and the date of Easter depends on the spring equinox and the phases of the moon.

The most famous of those letters are those authored by Athanasius, a collection of which was rediscovered in a Syriac translation in 1842. Festal Letters of other Bishops of Alexandria, including Cyril have also been preserved.