St. Euphemia, whose relics are in the middle reliquary, was born in Chalcedon (present-day Kadköy), the daughter of devout parents, Philophron and Theodosiani. She was tortured during the persecutions of Emperors Diocletian and Maximian in the late third century.
The Saint played a major role in inspiring the Fathers of the Fourth Ecumenical Council. During that council (451), St. Euphemia worked a miracle that determined the final doctrinal definition. The 630 Fathers, who gathered for this council in Chalcedon, were deliberating about the two natures of Christ. Eutyches and Dioscoros claimed that Christ possessed only a single nature. To test this teaching, the Holy Fathers inscribed the differing opinions on two separate decrees, which they placed inside the reliquary of St. Euphemia. When the reliquary was later opened, the decree of the heretics had fallen to the feet of the Saint, while the Orthodox doctrine rested in her hands. The Orthodox Church celebrates this miracle on July 11. The repose of St. Euphemia is commemorated on September 16.
According to her biography, the relics of St. Euphemia adorned many churches of Constantinople prior to its conquest in the fifteenth century. Thereafter, the relics were successively relocated to each of the Patriarchal churches. The icon of St. Euphemia records scenes from the life, martyrdom, and miraculous interventions of the Saint.
The palace of Antiochos was originally an early fifth-century secular building, and it seems to have been transformed into a church by the first half of the seventh century, when the body of St. Euphemia was enshrined there. The church, which came to be regarded as the martyrion of the saint after her body was enshrined there, was restored and redecorated more than once. The building was a domed hexafoil in plan, richly decorated, and boasting at various periods mosaics and frescoes.
The body of the martyr Euphemia was brought to the church for safety from her native Chalcedon across the Bosporus when that city was in danger of sack by the Persians, probably in 626, and thereafter became a very popular relic in the Byzantine capital, for the body still exuded blood. The body of St. Euphemia doubtless also developed an important cult because of the tradition that her body had chosen the declaration of faith of the Orthodox party at the Council of Chalcedon. The Council of Chalcedon was of course held in the martyrion of the martyr in Chalcedon, not in her Constantinopolitan martyrion, as the Russian Anonymous variant has it. The popularity of the relic caused it to be among the first casualties of Iconoclasm, and, coffin and all, it was thrown into the sea. Miraculously rescued by faithful iconodules on the island of Lemnos, the body of St. Euphemia was restored to her church at the hippodrome in the last years of the eighth century. The history of this relic is unclear after its reentombment in the church. By the late twelfth century it is located outside the city walls, and the church at the hippodrome claims only lesser relics of the Chalcedonian martyr, including her head and her empty tomb. After the Latin conquest of Constantinople, "relics" and the jewel-encrusted arm of St. Euphemia are reported in Germany, but there is no mention of the saint's head or body in the West. These relics must have somehow escaped the Latins and remained in Constantinople, the head at the church near the hippodrome (if we are to accept the testimony of the Russian Anonymous), and the body outside the city.
From Russian Travelers to Constantinople in the Fourteenth and Fifteenth Centuries, by George P. Majeska (Dumbarton Oaks, Washington DC, 1984) pp. 259-260.
Saint Euphemia's Conversation With Elder Paisios
More on the Relation Between Elder Paisios and Saint Euphemia
Apolytikion in the Third Tone
O Euphemia, Christ's comely virgin, thou didst fill the Orthodox with gladness and didst cover with shame all the heretics; for at the holy Fourth Council in Chalcedon, thou didst confirm what the Fathers decreed aright. O all-glorious Great Martyr, do thou entreat Christ God that His great mercy may be granted unto us.
Kontakion in the Second Tone
You made fervent effort in your struggles of trial, in your struggles of faith for Christ your bridegroom. But even now, intercede with the Theotokos that the heresies and insolence of enemies be trod beneath the feet of our rulers, O All Praised, who received and kept the Decree of the 630 God-bearing Fathers.