theologian and abbot of the Monastery of St. Catherine, on Mt. Sinai, whose writings, public disputes with various heretical movements in Egypt and Syria, and polemics against the Jews made him in his day a foremost advocate of orthodox Christian doctrine, specifically on the person and work of Christ, and provided key documents for the history of early Christian thought. By his leadership and eloquence he won the title “the New Moses.”

Of unknown origin and sometimes confused with others of the same name, including the early 7th-century Orthodox patriarch of Antioch, Anastasius periodically descended from his Mt. Sinai community to refute the ideas of theological dissidents. In his principal work, Ho dēgos (c. 685; “The Guide”), he marshalled arguments against the Monophysites (monophysite), a heretical sect believing that Christ comprised a single, divine nature that subsumed his humanity. The faulty transmission of the original text caused it to be attributed to other Syrian authors, and only through later research has its true source been determined. Drawn up in the desert, “The Guide” is flawed by unverified citations and paraphrased references to texts from the early Church Fathers, formulas from church councils, and Aristotelian concepts applied to the analysis of the Christological problem, all quoted from memory. In this work Anastasius cites himself in other writings now lost: a comprehensive “Essay on Christian Dogma”; an “Apology for Christianity”; and a treatise “Against Nestorius,” the 5th-century heretical theologian who proposed that Christ's humanity subsisted autonomously from his divinity.

Anastasius' other notable extant writings include a survey of heresies prominent in his time, “Exposition on Faith,” and “Questions and Answers,” reedited by a later author and largely devoted to the relation of monastic life to secular culture. Anastasius' “Commentary on the Six Days of Creation” shows a tendency toward Alexandrian allegorical biblical exegesis and interprets the book of Genesis as directly signifying Christ and the church. Two tracts on the creation of man in the intellectual and spiritual image of God show the same tendency. In them is the earliest recorded reference to the doctrinal controversy on Monothelitism, the condemned teaching that only a divine volition was operative in Christ. Shorter works on worship, the communion of the Lord's Supper, and mystical prayer exhibit the Aristotelian method in depicting the psychology of learning and the spiritual nature of the mind and its orientation toward ultimate truth and beauty.

Some scholars credit Anastasius with contributing to the collection of texts known as “The Doctrine of the Fathers on the Incarnation of the Word (Son of God).”