Commemorated May 30
According to some accounts, Isaac was a Syrian, but this is uncertain. Certain details about his early life are unknown but history records that Isaac had been a hermit living in a small hut in the wilderness outside of Constantinople. In the year 378, when he heard that the Roman emperor Valens had fallen into the heresy of Arianism and was persecuting the Nicene Christians, deposing bishops, closing some churches, and turning others over to the Arians, Isaac went into the imperial city to confront the emperor. At the time, Valens was preparing a military campaign against the Goths. After several attempts to dissuade the emperor from his persecutions, Isaac prophesied that Valens would "die in flames" because of his actions. The emperor ordered that Isaac be thrown into prison, vowing that he would punish Isaac and put him to death upon his return from battle. Soon after, on August 9, 378, Valens was defeated at the Battle of Adrianople and died in a fire after taking refuge in a barn.
Valens' successor, the Emperor Theodosius I, released Isaac, outlawed Arianism and reopened the churches closed by Valens. Isaac wanted to return to monastic life in the wilderness, but a wealthy aristocrat named Saturninus built a monastery for Isaac in Constantinople, over which he became the first hegumen (abbot). Isaac is also known as a zealous defender of Christian orthodoxy at the Second Ecumenical Council, convened in Constantinople in 381.
At the end of his life, Isaac entrusted the leadership of the monastery to his closest disciple, Dalmatus, who was later himself glorified (canonized as a saint), and after whom the monastery came to be known as the Dalmatian Monastery. Isaac died in his monastery on May 30, 383, although others place his death around 396. The life of John Chrysostom includes mention of St. Isaac living into the fifth century.
