March 21 in Eastern Orthodox liturgical calendars is a feast day and a day of commemoration of saints and martyrs. Although some Orthodox churches use the Revised Julian Calendar and others use the traditional Julian calendar, the fixed commemorations for their respective March 21 are broadly the same, no matter which calendar is used.
Martyrs Philemon and Domninus of Thessalonica, in Italy. (see also: March 26)
Saint Maria the Martyr, in Perge.
Saint Serapion, Bishop of Thmuis, Egypt (c. 358)
Venerable Serapion the Sindonite, monk of Egypt (5th century) (see also: May 14)
Saint Sophronius, Abbot of the Monastery of St. Theodosius, in Palestine (542)
Saint Thomas, Patriarch of Constantinople (610)
Venerable Jacob the Confessor (James the Confessor), Bishop, of the Studion (late 8th century)
Saint Beryllus, Bishop of Catania (c. 90)
Saint Lupicinus of Condat, desert-dweller of the Jura Mountains, Gaul (480)
Saint Enda of Aran, Abbot of Arranmore, monk, earliest leader of Irish monasticism (530)
New Martyr Michael of Agrapha (Michael of Soluneia), at Thessalonica (1544 or 1547)
Venerable Seraphim of Vyritsa (1949)
New Hieromartyr Vladimir Vvedensky, Priest (1931)
New Hieromartyr Theodore (Pozdeyevsky), Archbishop (1938) (see also: October 10)
Glorification of Venerable Pachomius, Abbot, of Nerekhta (1384) (see also: May 15)
March 21/April 3. Orthodox Calendar (PRAVOSLAVIE.RU).
April 3 / March 21. HOLY TRINITY RUSSIAN ORTHODOX CHURCH (A parish of the Patriarchate of Moscow).