The Monk Isaac lived during the fourth century, accepted monastic vows, and pursued asceticism in the wilderness.
During the years of the reign of the emperor Valentus (364-378), a zealous adherent of the Arian heresy, they began to persecute the Orthodox, closing and destroying churches. Having learned of the persecution, the Monk Isaac quit the wilderness and arrived in Constantinople, so as to console and encourage the Orthodox. At this time, barbarian Goths, dwelling along the River Danube, were making war against the empire. They seized Thrace and advanced towards Constantinople.
When the emperor Valentus was leaving the capital with his soldiers, the Monk Isaac, turning himself towards the emperor, loudly cried out: “Emperor, unlock the churches of the Orthodox, and then the Lord will aid thee!” But the emperor, disdaining the words of the monk, confidently continued on his way. Three times did the monk repeat his request and prophecy. The angry emperor gave orders to hurl the Monk Isaac into a deep ravine, grown over with prickly thorns. By day the ravine was a swamp, and to emerge from it was impossible. But the monk with the help of God remained alive, and he emerged, overtook the emperor and said: “Thou wanted to destroy me, but the holy Angels did save me from peril. Hear me, open up the churches to the Orthodox and thou shalt defeat the enemy. If however thou dost not heed me, then thou shalt not return alive, but shalt perish in fire.” The emperor was astonished at the boldness of the monk and ordered his attendants Saturninus and Victor to take the monk and hold him in prison until his return.
The prophecy of the saint soon happened. The Goths defeated and began to chase down the Greek army. The emperor together with his Arian generals took refuge in a barn with straw, and the attackers set it afire. After receiving news about the perishing of the emperor, they set free the Monk Isaac and began to honour him as a prophet of God.
Onto the throne was then chosen the holy Emperor Theodosius the Great (379-395), who on the advice of Saturninus and Victor summoned the elder to himself, meeting him with great respect, beseeching prayers to the saints and fulfilling all his instructions: he banished the Arians from Constantinople and restored the churches to the Orthodox.
The Monk Isaac wanted to return into the wilderness, but Saturninus and Victor besought him not to leave the city, but rather to protect it with his prayers. In the outskirts of Constantinople they built for the saint a hut, where monks gathered to him. Thus arose a monastery, the hegumen and spiritual guide of which was the Monk Isaac. He nourished also the laypeople, and helped many of the poor and suffering. Having reached extreme old age, the Monk Isaac made co-hegumen together with him the Monk Dalmatos, by whose name the monastery was called. The Monk Isaac died in the year 383, and his memory is celebrated also on 22 March.