63 Flavius Anastasius (Greek: Φλάβιος Ἀναστάσιος) or Anastasius I (Ἀναστάσιος A), was the emperor of the Eastern Roman (Byzantine) empire from 491 to 518.

Flavius Anastasius (Greek: Φλάβιος Ἀναστάσιος) or Anastasius I (Ἀναστάσιος A), was the emperor of the Eastern Roman (Byzantine) empire from 491 to 518. A non-Chalcedonian himself, his attempts at reconciling the Christological differences between the Chalcedonians and non-Chalcedonians was unsuccessful

Anastasius was born at Dyrrhachium (now Durres, Albania) about the year 430. His parents were Pompeius, a nobleman of Dyrrhachium, and Anastasia Constantina. His mother was an Arian. Anastasius had one eye black and one eye blue (heterochromia), and for that reason was nicknamed Dicorus (Greek: Δίκορος, "two-pupiled").

Although not prominent, Anastasius was a member of emperor Zeno's court, holding the position of silentiarius. Apparently he was well educated, particularly in theology such that he was considered in 488 for the position of bishop of Antioch. After the death of emperor Zeno in 491, his widow empress Ariadne supported Anastasius as Zeno's successor, even preferring him over Zeno's brother Longinus who had hoped to become emperor.

Anastasius was acclaimed emperor on April 11, 491, and a month later he married Ariadne on May 20 apparently on the initiative of Ariadne, despite his advanced age. Anastasius was 61. After ascending the throne, Anastasius exiled Longinus to Egypt and expelled many officials, especially Isaurians, from Constantinople. It took until 498 for him the suppress the Isaurian revolt following their expulsion. Anastasius was also confronted by hostilities in the Balkans and with the Persians throughout most of his reign.

While early on Anastasius' beliefs were strongly Miaphysite, his ecclesiastical policy was moderate. He was a strong supporter of the Henoticon of Zeno and tried to reconcile the Chalcedonians and non-Chalcedonians. His Miaphysite stand brought about tensions with the strongly Chalcedonian Patriarch of Constantinople, Euphemius, resulting in the exile of Euphemius in 496. Euphemius' successor, the Chalcedonian Macedonius II, in turn was replaced by Anastasius in 511 with the Monophysite patriarch, Timothy I. In 512, Anastasius also appointed the Monophysite Severus as patriarch of Antioch.

Anastasius' actions in 511 and 512 of seating non-Chalcedonians in Constantinople and Antioch sees provoked riots and rebellion that nearly overthrew his government, unrest that was not subdued until 515. In 516, Anastasius attempted to replace the Patriarch of Jerusalem with a non-Chalcedonian, but he did not force the issue after riots broke out in Jerusalem after the announcement.

In spite of his non-Chalcedonian policies, Anastasius was not seen by the non-Chalcedonians as one of their own. His policies contributed to the ever-deepening rift that in 518, the year he died, the Miaphysite Council of Tyre solidified the doctrinal position of those who became known as Syrian Jacobites.

Anastasius died in Constantinople on July 9, 518 at the age of 88, and was buried at the Church of the Holy Apostles with his wife, Ariadne. He left no children.