The Placing of the Venerable Belt of the Most Holy Theotokos in a church of Constantinople’s Chalcoprateia district took place during the reign of the emperor Theodosius the Younger. Before this the holy relic, entrusted to the Apostle Thomas by the Mother of God Herself, was kept by pious Christians at Jerusalem after Her Dormition. During the reign of Emperor Leo, the Wise (886-911), his wife Zoe was afflicted with an unclean spirit, and he prayed that God would heal her.
The empress had a vision that she would be healed of her infirmity if the Belt of the Mother of God were placed upon her. The emperor then asked the Patriarch to open the coffer. The Patriarch removed the seal and opened the coffer in which the relic was kept, and the Belt of the Mother of God appeared completely whole and undamaged by time. The Patriarch placed the Belt on the sick empress, and immediately she was freed from her infirmity. They sang hymns of thanksgiving to the Most Holy Theotokos, then they placed the venerable Belt back into the coffer and resealed it.
In commemoration of the miraculous occurrence and the twofold Placing of the venerable Belt, the Feast of the Placing of the Venerable Belt of the Most Holy Theotokos was established. Parts of the holy Belt are in the Vatopedi monastery on Mt. Athos, in Trier monastery, and in Georgia.
~Greek Orthodox Patriarchate of Antioch and All the East, https://www.antiochpatriarchate.org/en/page/the-placing-of-the-honorable-sash-of-the-most-holy-theotokos/720/.
Although the historical accounts differ somewhat, the Deposition that is celebrated today took place most likely during the reign of Emperor Arcadius (395-408), when the precious Cincture of the Mother of God was brought from Zela of Cappadocia to Constantinople, and placed in the Church of the Theotokos in the section of Chalcopratia.
Apolytikion of Venerable Sash of the Theotokos
Plagal of the Fourth Tone
O Ever-Virgin Theotokos, shelter of mankind, thou hast bestowed upon thy people a mighty investure, even thine immaculate body’s raiment and sash, which by thy seedless childbirth have remained incorrupt; for in thee nature and time are made new. Wherefore, we implore thee to grant peace to the world, and great mercy to our souls.
Kontakion of Venerable Sash of the Theotokos
Thy precious sash, O Theotokos, which encompassed thy God-receiving womb, is an invincible force for thy flock, and an unfailing treasury of every good, O only Ever-virgin Mother.
~Greek Orthodox Archdiocese of America (GOA), https://www.goarch.org/chapel/saints?contentid=184.