The very miraculous icon of the Most Holy Theotokos and Virgin Maria, the "Axion Esti". This is a copy from the original icon that the miracle happened.
According to tradition, an elder and his disciple lived in in a cell on Mount Athos. One Saturday night the elder left to attend the All-Night Vigil in the Protaton of Karyes. He told his disciple to chant the service alone. That evening an unknown monk who called himself Gabriel, came to the cell, and they began the Vigil together. During the ninth ode of the canon (the Magnificat), the disciple began to sing "My soul magnifies the Lord..." with the Irmos of St. Cosmas the Hymnographer (October 14), "More honorable than the Cherubim..."
The stranger sang the next verse, "For He has regarded the low estate of His handmaiden..." Then he chanted something the disciple had never heard before, "It is truly meet to bless Thee, O Theotokos, ever-blessed and most pure, and the Mother of our God." Then he continued with, "More honorable than the Cherubim..." When the disciple asked the visiting monk to write the words of the new hymn down, he took a roof tile and wrote on it with his finger, as though the tile were made of wax. The disciple knew then that this was no ordinary monk, but the Archangel Gabriel.
At that moment the angel disappeared, but the icon of the Mother of God continued to radiate light for some time afterward. The Eleousa ("merciful") icon of the Virgin Mary, before which the hymn "It Is Truly Meet" was first chanted, was transferred to the katholikon (main church) at Karyes, known as the Protaton. The tile, with the hymn written on it, was taken to Constantinople when St. Nicholas II Chrysoberges was Patriarch (984-996). Since that time the icon has been considered the protector of the Holy Mountain and its holiest icon.