Intercession of the Theotokos
According to Eastern Orthodox Sacred Tradition, the apparition of Mary the Theotokos occurred during the 10th century at the Blachernae church in Constantinople (modern-day Istanbul) where several of her relics (her robe, her veil, and part of her belt) were kept.
On Sunday, October 1 at four in the morning, St. Andrew the Blessed Fool-for-Christ, who was a Slav by birth, saw the dome of the church open and the Virgin Mary enter, moving in the air above him, glowing and surrounded by angels and saints.
The Virgin Mary asked Her Son, Jesus Christ, to accept the prayers of all the people entreating Him and looking for Her protection.
The icon of the feast, which is not found in Byzantine art, depicts in its upper part the Virgin Mary surrounded by a luminous aureole.
The Feast of the Intercession commemorates the miracle as a joyous revelation of the Theotokos' protection, which is spread over the world, and the Mother of God's great love for mankind.
As a legend has it,[6] each of their campaign the Cossacks began with Sub tuum praesidium prayer to the Holy Lady (in Ukrainian: «Під Твою милість прибігаємо, Богородице Діво, молитвами нашими в скорботах не погордуй, але від бід ізбав нас, єдина чиста і благословенна!»), by which making reference to the Intercession.
Notably, an icon in the National Art Museum of Ukraine shows the Virgin Mary protecting the Ukrainian cossack hetman Bohdan Khmelnytsky.
The singular (as compared to the rest of the Christian world) devotion of Ukrainians to the Intercession feast (for them being the third important, after Easter and Christmas, holiday) was acknowledged in Pylyp Orlyk Constitution, where Christmas, Easter and 'Pokrova' were set to be the three designated annual days of convention by the supreme cossack council that was supposed to rule the country.
The tradition was referred to again in XX century, when the founding of the Ukrainian Insurgent Army was attributed (although retrospectively and probably inaccurately) to October 14, 1942.
It is not a part of the ritual traditions of, and therefore is not celebrated by, the Oriental Orthodox Churches or some jurisdictions that allow Western Rite Orthodoxy.
[8] The other one is the Church of Intercession in Bogolyubovo near Vladimir on the Nerl River (Russian: Церковь Покрова на Нерли, romanized: Tserkov Pokrova na Nerli).
Both churches are on the United Nations' World Heritage List, the latter as part of the site White Monuments of Vladimir and Suzdal.
