Venerable Ioannikios the Great

Venerable Ioannikios was born around 752 in the Bithynian village of Marikatou. He served in Constantinople's elite palace guard (the exkoubitoi) from around 780/781 and took part in campaigns against the Bulgarians. He distinguished himself with heroic conduct at the Battle of Marcellae on July 20, 792, during a Byzantine defeat.

Raised in an iconoclast military milieu common under Emperors Constantine V and Leo IV, after the restoration of icon veneration at the Second Council of Nicaea (787) he underwent a miraculous encounter with a hermit-monk who rebuked him for professing faith in Christ while despising His icon — this precipitated his repentance and firm turn to icon veneration, which he thereafter defended vigorously, becoming a staunch opponent of the second wave of iconoclasm under Emperors Leo V and Theophilos.

After the 792 battle, despite the imperial honors offered him, he abandoned military life and withdrew to Mount Olympus in Bithynia, where he spent about 21 years in strict asceticism — first at the Agavur monastery, later settling at the Antidion monastery, alternating periods of eremitic life and reclusion.

He became renowned for the gift of prophecy (foretelling the deaths of iconoclast emperors and the eventual restoration of icon veneration in 843), healings, walking on water, power over wild beasts, and a miracle bringing forth a healing spring from barren ground. His Life was composed by the monks Peter and Sava.

He reposed on November 4, 846, at the Antidion monastery on Mount Olympus, at the age of 94.