The Holy Martyr Merkurii of Smolensk was a Slav by birth, probably from Moravia, the descendant of a princely line. Brought up in Orthodoxy, Saint Merkurii in zeal for the true faith set off from his own native land to Rus', where he served in the army of the Smolensk prince. The saintly soldier secretly led an ascetic life – he was strict in fasting, chaste, spending his nights at prayer, and spiritually preparing himself to suffer for faith in Christ. In the year 1239 an horde of Tatars (Mongols), having already laid waste to many a Russian city, appeared in the vicinity of Smolensk and set up camp 25 versts from it at Dolgomost', threatening with ruin the city and its holy places. A church-warden, praying by night in the Smolensk cathedral in front of a wonderworking image of the Mother of God, heard the voice of the Queen of Heaven, commanding him to find the holy warrior and say to him: "Merkurii, go forth into military foray, as the Sovereign Lady doth summon thee". The soldier himself came into the cathedral and heard the voice of the All‑Pure Virgin, sending him to fight the enemy and promising him Heavenly help.
The warrior of Christ set off that very night to the Tatar camp at Dolgomost'. He fought there with the leader of the Tatar army – a giant possessed of immense strength. He killed him and entered into single-combat with the enemy host. Invoking the Name of the Lord and of the All-Pure Mother of God, the holy warrior destroyed many of the enemy. The Tatar warriors watch with terror as lightning-bearing men and a radiant Woman aided Saint Merkurii in the fight, and unable to stand up against the warrior of Christ, they retreated in flight. Saint Merkurii in the battle was himself killed by the son of the Tatar giant killed by him.
The inhabitants of Smolensk, saved through the miraculous intervention of the Lord and the MostHoly Mother of God, reverently buried the body of the soldier-martyr in the cathedral of the Dormition of the MostHoly Mother of God. Soon after his death, Saint Merkurii appeared in a vision to the church-warden and ordered that his armour be hung over the grave, promising the Smolensk people constant help and intervention in every sorrow and struggle. Even now at present in the Smolensk cathedral church are still preserved the sandals of the holy Martyr Merkurii. The festal celebration to him was established at the end of the XVI Century, and already in 1509 the inhabitants of Smolensk were calling him their especial patron.