May 21 (Eastern Orthodox liturgics)
May 20 - Eastern Orthodox Church calendar - May 22
All fixed commemorations below are celebrated on June 3 by Orthodox Churches on the Old Calendar.
For May 21st, Orthodox Churches on the Old Calendar commemorate the Saints listed on May 8.
Saints
Holy Equals-to-the-Apostles Emperor Constantine, and Empress Helena, his mother- Martyrs Polyeuctus, Victorinus, and Donatus, at Caesarea in Cappadocia.
- Hieromartyr Secundus and those with him, in Alexandria
- Saint Adelphios, Bishop of Onouphis, in Byzantine Egypt
- Saint Boros, monk.
- Saint Christopher I, Patriarch of Antioch
Pre-Schism Western saints
- Hieromartyrs Timothy, Polius and Eutychius, deacons, in Mauretania Caesariensis.
- Hieromartyr Valens and Companions, Bishop who was martyred in Auxerre in France along with three children.
- Martyr Secundinus, in Cordoba in Spain under Diocletian
- Saint Hospitius the Hermit of Nice, Wonderworker
- Saint Barrfoin of Killbarron
- Saint Gollen of Denbighshire, a saint who has given his name to Llangollen in Wales
- Saint Isberga of Aire, reputed sister of Charlemagne, nun at Aire in the Artois, of which she is the patroness
- Saint Ageranus of Beze, a monk at Bèze in France, martyred by the Vikings
- Saint Theobald, Archbishop of Vienne
Post-Schism Orthodox saints
Blessed Constantine, prince, and his children Michael and Theodore, Wonderworkers of Murom- Saint Cyril II, Bishop of Rostov
- Saint Basil of Ryazan, Bishop
- Saint Helen of Decani, Serbia, Princess Venerable Cassian the Greek, monk of Uglich, Wonderworker
- Saint Agapitus of Markushev the Hieromartyr, Abbot
- Saint Constantine the Fool-for-Christ, of Novotorzanin, Russia
- New Martyrs King Constantine Brancoveanu of Wallachia and his four sons Constantine, Stephen, Radu, and Matthew, and his counsellor Ianache
- Martyr Pachomios of Patmos
New martyrs and confessors
Synaxis of Hieromartyrs of Karelia.Synaxis of Hieromartyrs of Ufa.Other commemorations
- Uncovering of the relics of St. Andrew Ogorodnikov, fool-for-Christ of Simbirsk
- Repose of Elena Pavlova of Chepel, Kharkiv
- Repose of Elder Isaac of Dionysiou Monastery of Mount Athos
- The Anastenaria fire-walking ritual is performed from May 21–23 in some villages in Northern Greece and Southern Bulgaria, coinciding with the feast of Constantine and Helen.
- Synaxis of all saints of Karelia,
Icons
Synaxis of the "Vladimir" Icon of the Most Holy Theotokos- Synaxis of the "Virgin of Tenderness" Icon of the Most Holy Theotokos from Pskov-Pechersk