Holy Virgin Mary's cover is a holiday celebrated mostly in Russian Orthodoxy. In Russian Orthodoxy it's a great holiday and has a fixed date - October, 14 (October, 1 - Julian calendar).
In 910 (according to some sources, in 902), the Emperor Leo the Wise and Patriarch Macarius, the Byzantine Empire was at war with the Saracens - Muslims, and Constantinople was in danger. On Sunday, October 1 at the time of vigil, when Vlaherna temple was crowded with worshipers, among whom was Andrew, fool-for-Christ - Slav, a young man who was captured and sold into slavery in Constantinople local resident Feognost. In the fourth hour of the night, raising his eyes to heaven, Andrew saw walking on air Holy Mother of God, illumined by heavenly light and surrounded by a host of angels and saints, the Virgin Mary was accompanied by John the Baptist and John the Evangelist. Holy Mary was praying for people here for a long time and the teardrops was falling all over Her cheeks. Then, at the end of Her prayers, Mary put the cover from Her head off and spread out over all the people stood. While Holy Mary was there, her cover was there too. But when she disappered - it disappeared as well. But taking it with Her, She left the grace of it for those who were there.
