thumb|The cathedra of the [[Pope in the apse of St. John Lateran, the cathedral church of Rome]]
thumb|Modern cathedra at the [[Cathedral of Our Lady of the Angels in Los Angeles]]
thumb|19th-century cathedra in [[Lichfield Cathedral]]
A cathedra is the throne of a bishop, found in the cathedral church of their diocese. The word derives from the Greek (), meaning "seat", especially one used by a bishop or teacher; this term is also the ultimate source of the word "chair".
Cathedrae apostolorum
The term appears in early Christian literature in the phrase cathedrae apostolorum, indicating authority derived directly from the apostles.
Ex cathedra
The doctrine of papal infallibility, the Latin phrase ex cathedra (literally, "from the chair") was proclaimed at the First Vatican Council by Pius IX in 1870 as meaning "when, in the exercise of his office as shepherd and teacher of all Christians, in virtue of his supreme apostolic authority, the Bishop of Rome defines a doctrine concerning faith or morals to be held by the whole Church."
Cathedrals as a bishop's seat
Eventually, the main church of a diocese, used as the primary church by its bishop, received the title "cathedral". The cathedral is literally the church into which a bishop's official cathedra is installed.
The Joint International Commission for Theological Dialogue Between the Catholic Church and the Orthodox Church makes use of the term cathedral to point out the existence of a bishop in each local church, in the heart of ecclesial apostolicity.
Notable examples
===Cathedra Petri===<!-- This section is linked from Gian Lorenzo Bernini -->
thumb|[[Bernini's massive sculptural reliquary for the Cathedra Petri or "Chair of Peter" in St. Peter's Basilica, Rome]]
The definitive example of a cathedra is that encased within the Triumph of the cathedra Petri designed by Gian Lorenzo Bernini in 1657, and completed and installed in St Peter's Rome in 1666. As early as the 8th century, an ancient wooden chair overlaid with ivory plaques depicting The Twelve Labours of Heracles and some of the constellations, was venerated as the episcopal chair of St. Peter. It is a Byzantine throne with framed fragments of acacia wood, encased in the oak carcass and reinforced with iron bands. It was long believed to have been used by the Apostle Saint Peter, but the Holy See recognises that the chair was a gift from Holy Roman Emperor Charles the Bald to Pope John VIII in 875. Several rings facilitated its transportation during processions. Pope Alexander VII commissioned Bernini to build a monument to display this relic in a triumphant manner. Bernini's gilded bronze throne, richly ornamented with bas-reliefs, encloses the relic. On January 17, 1666, it was solemnly set above the altar of Saint Peter's Basilica in Vatican City. Greater than life-sized sculptures of four Doctors of the Church form an honour guard: St. Ambrose and St. Athanasius on the left, and St. John Chrysostom and St. Augustine on the right.
Celebrated on February 22 in accordance with the calendar of saints, the Feast of Cathedra Petri (the Feast of the Chair of Peter the Apostle) honours the founding of the church in Rome and gives thanks for the work of Saint Peter.
Chair of Bishop Maximianus
A fifth- or sixth-century bishop's throne decorated with elaborate ivory carving is preserved in the sacristy of the cathedral at Ravenna. It bears a monogram in front, "Maximianus ep.", which gave it its name. The identity of the bishop is given by the 1908 Catholic Encyclopedia as Maximianus of Constantinople (d. 431), considered as more likely than Maximianus of Ravenna (d. 556). Since the Middle Ages, it has always been used in the triple enthronement of an Archbishop of Canterbury. He is seated on the throne in the quire as Diocesan Bishop, in the chapter house as titular abbot, and in St. Augustine's chair as Primate of All England. This is the only occasion in which the cathedra is used. A second cathedra is used for other occasions at which the archbishop is present.
Placement
The early Christian bishop's throne, or cathedra, stood in an elevated position behind the altar, near the wall of the apse.