May 10 – Eastern Orthodox Church calendar – May 12

All fixed commemorations below celebrated on May 24 by Orthodox Churches on the Old Calendar.^{[note 1]}

For May 11th, Orthodox Churches on the Old Calendar commemorate the Saints listed on April 28.

• Martyr Evellius, under Nero (66)^[1][2]
• Martyrs Maximus, Bassus, and Fabius (284–305)^[2][3]
• Hieromartyr Mocius (Mucius), presbyter of Amphipolis in Macedonia, beheaded in Byzantium (288)^{[4][note 2]}
• Martyr Armodius^{[5][note 3]}
• Martyr Acacius of Lower Moesia^[6]
• Saints Cyril and Methodius, Equal-to-the-Apostles and Enlighteners of the Slavs (869, 885)^[7][8] (see also: July 17 )
• Saints Clement of Ohrid (916), Sabbas (10th century), Angelarius (Angelyar) (ca. 886), Gorazd (896), and Naum of Preslav (910) — Disciples of Saints Cyril and Methodius and missionaries of the Slavs, Wonderworkers and Equal-to-the-Apostles^{[9][note 4]}
• Saint Rostislav the Prince of Great Moravia, Confessor of the Faith (870)^[6][8] (see also: October 29)

• Hieromartyr Anthimus of Rome, and martyrs Sisinius the deacon with Diocletius and Florentius (disciples of St. Anthimus), (284–305)^[2][11][12]
• Saint Principia of Rome, a holy virgin in Rome and disciple of St Marcella (420)^[12]
• Saint Mammertus, Archbishop of Vienne (475)^[12][13]
• Saint Possessor of Verdun, Bishop of Verdun, he and his flock were greatly troubled by the barbarian invasions of Franks, Vandals and Goths (c. 486)^[12]
• Saint Tudy (Tudinus, Tegwin, Thetgo), a disciple of St Brioc in Brittany (5th century)^[12]
• Saint Credan of Cornwall, hogherd.^[14]
• Saint Gangulphus (760)^[12]
• Saint Fremund of Dunstable, Anglo-Saxon hermit, killed by his kinsman Oswy with the help of Danish invaders who had also murdered King Edmund (866)^[12]
• Saint Odo of Cluny, the second Abbot of Cluny (942)^[12]
• Saint Mayeul (Majolus, Maieul), Abbot of Cluny (994)^[6][12]
• Saint Odilo of Cluny (1049)^[12]

• Martyrs Olympia, abbess of Mytilene, and nun Euphrosyne (1235)^[6][15]
• Saint Sophronius of the Kiev Caves, recluse (13th century)^{[6][16][17][note 5]}
• Saint Nicodemus of Pec, Archbishop of Serbia (1324)^[6][18]
• Hieromartyr Joseph, first Metropolitan of Astrakhan (1672)^[6][19][20]
• Blessed Christopher of Georgia (Christesias), monk at the Monastery of St. John the Baptist, at the David Gareja monastery complex, "The Thebaid of Georgia" (1771/1871)^{[21][22][note 6]}
• New Martyr Dioscorus (Dioscorides) the New, of Smyrna^[6][23][24]
• New Martyr Argyrus (Argyrus, Argyres) of Thessalonica (1806/1808)^[6][24][25]
• Saint Theophylact, bishop of Stavropol and Ekaterinodar (1872)^[26]

• Commemoration of the Founding of Constantinople (330) as Capital of the Roman Empire^[29][30]
• Consecration of the Saint Sophia Cathedral in Kiev (960).^[31]

• Saints Saints Cyril and Methodius, Equals-to-the-Apostles.
• St. Clement of Ohrid.
• Saint Naum of Preslav.
• St. Rostislav the Prince of Great Moravia, Confessor of the Faith.
• St. Mamertus, Archbishop of Vienne.
• Sancreed church and war memorial, Cornwall.
• St. Gangulphus of Burgundy.
• St. Odo of Cluny.
• St. Odo of Cluny.
• St. Majolus of Cluny.
• Saint Sophia Cathedral in Kiev.