On the 8th of June we commemorate the Synaxis of the Most Holy Theotokos and the Archangel Michael in the Sosthenion district of Constantinople.
The Michaelion was one of the earliest and most famous sanctuaries dedicated to the Archangel Michael in the Roman Empire. According to tradition, it was built in the fourth century by Emperor Constantine the Great (306-337) over an ancient pagan temple called the Leosthenion or Sosthenion, erected by the Argonauts and dedicated to Zeus Sosthenios or a winged deity. According to tradition, Constantine interpreted the winged statue of the temple as a Christian angel. After sleeping the night in the temple, Constantine reported a vision that the angel was the Archangel Michael, and converted the building into a church to honor him. In the early fifth century the historian Sozomen recorded the devotions by the crowds at the Michaelion and wrote of first-hand reports of healings at the Michaelion, stating that he had himself received a healing. The pagan temple which had existed there had been previously associated with healing and medicine, and the Christians continued to associate the location and the Michaelion with its healing waters.
The Michaelion was a magnificent church and became a model for hundreds of other churches in Eastern Christianity. It also had a chapel dedicated to the Theotokos. It was located just north of Constantinople, in the village of Sosthenion (modern İstinye) on the European shore of the Bosphorus strait. The Archangel Michael slaying a serpent became a major art piece at the Michaelion and eventually lead to the standard iconography of the Archangel Michael as a warrior. After the construction of the church, four other churches in honor of the Archangel Michael followed it in Constantinople. During the reign of the next several emperors after Constantine, the number of churches dedicated to the Archangel Michael in Constantinople increased to fifteen.
By the late ninth century, the church had fallen in ruin, until it was rebuilt by Emperor Basil I the Macedonian (867–886). As an imperial foundation, it soon eclipsed its rival at Anaplous. A monastery was attached to the church at an unknown later date. It is first securely attested in the eleventh century and is continuously mentioned until 1337. French scholar Raymond Janin hypothesizes that it was demolished in the fifteenth century, and its material used in the construction of the nearby Rumelihisarı fortress.