Origins and early life
Marcellus was born in the city of Apamea in Syria. His parents were wealthy, but they died while he was still young, leaving him an orphan. He received his education first at Antioch and then at Ephesus. Rather than retain the property left to him, he distributed all of his inherited possessions to the poor, severing his ties to the world. Under the guidance of an experienced elder at Ephesus he took up the ascetic life, and afterward traveled to Constantinople, where he sought entrance to the monastery of Saint Alexander, who accepted him and tonsured him into the monastic schema.
The Monastery of the Unsleeping Ones
The community Marcellus joined took its name — the Akoimetoi, or 'Unsleeping Ones' — from its central practice: psalmody was offered continuously, both day and night, by groups of monks who relieved one another in turn so that the praises of God never ceased. According to the sources, the monks were organized into companies according to the language they spoke — Greek, Latin, and Syriac — each company taking its turn at the services, so that every hour of the day and night was given over to God's glory. The order had been established around 425 by Alexander the Acoemete, and its houses spread, with a great monastery (the Irenaion) on the eastern shore of the Bosphorus. The community is also remembered as the source of the famed Studion (Studium) monastery in Constantinople, which was founded with monks drawn from it.
Abbot of the community
After the death of Saint Alexander and the tenure of his successor, Abba John, Marcellus was chosen as abbot (igumen) of the monastery against his own wishes — the third to lead the community. He is said to have remained in this office for some sixty years. Under his direction the Monastery of the Unsleeping Ones flourished as a center of monastic life, drawing monks from across the Empire. The sources attribute to him the gift of clairvoyance and a number of miracles: he is said to have healed the sick, cast out demons, and calmed storms, and tradition relates that when a sick disciple called to him in his mind from afar, Marcellus perceived it within the monastery and prayed for him.
The Council of Chalcedon
Marcellus took part in the Fourth Ecumenical Council, held at Chalcedon in 451, where he is remembered for defending the Orthodox faith against the Monophysite position, both at the Council itself and in the years that followed. The Acoemetae as a community were prominent in the Christological controversies of the fifth and sixth centuries, supporting the Chalcedonian confession.