a principal proponent of orthodoxy in the Christological controversy (a dispute centring on the nature and person of Christ) and one of the fathers of Palestinian monasticism.

Introduced to the ascetic life about 451 by Simeon the Stylite near Antioch and by others at the convent of David's Tower at Jerusalem, Theodosius in 455 entered the monastery of the Theotokos south of Jerusalem. After being made administrator by the community's benefactress, he resigned from the office in order to lead a solitary life at the Cave of the Magi, Metopa, near Bethlehem. From 460 to 470 the influx of followers was great enough to warrant construction on an adjoining plateau of a large coenobium (Latin: “monastic convent”), whose discipline integrated arts and crafts with the ascetic life. The popularity of the foundation attracted pilgrims and travelers for whose convenience Theodosius, with material aid from Byzantine officials, erected hostels and shelters for the aged, the poor, and the insane. The monastic community of about 400 was composed of Greeks, Slavs, and Armenians who performed prayer exercises in their separate languages but who celebrated the Greek liturgy of the Lord's Supper together. Theodosius' ascetic fame earned him election in 493 as archimandrite (monastic superior) of all convents in the Jerusalem area.

With his patriarchal colleague, St. Sabas, Theodosius induced the monastic and lay population of Palestine to resist the attempts of influential Eastern churchmen and Byzantine princes to impose the heresy of the Monophysites (monophysite) (those who believed that Christ had one, essentially divine nature, rather than both human and divine natures). He was consequently exiled by the Byzantine emperor Anastasius I in 517 but returned to continue his convent's development after Anastasius' death in 518. Destroyed in the 15th century, the monastery of St. Theodosius was rebuilt by the Greek monks of Jerusalem at the beginning of the 20th century.