Only-Begotten Son (Ancient Greek: Ὁ Μονογενὴς Υἱὸς, Russian: Единородный Сыне, Ukrainian: Єдинородний Сине, Old Armenian: Միածին Վորդի), sometimes called "Justinian's Hymn", the "Anthem of Orthodoxy" and/or the "Hymn of the Incarnation", is an ancient Christian hymn that was composed prior to the middle of the 6th century.
It is still currently used as a mournful hymn during the service of Great Friday in the Coptic Orthodox Church of Alexandria, with its length exceeding 10 minutes due to its long and deep melismatic nature.
During the controversy caused by the Origenists, Emperor Justinian declared that this hymn should be sung in all Christian Churches.
[5] Only-Begotten Son and Immortal Word of God, Who for our salvation didst will to be incarnate of the holy Theotokos and Ever-Virgin Mary; Who without change didst become man and was crucified; Who art one of the Holy Trinity, glorified with the Father and the Holy Spirit: O Christ our God, trampling down death by death, save us!
The term Monogenes is also found in the Nicene Creed as established by the First Ecumenical Council in 325 AD.