A cathedra (Latin, "chair", from Greek, kathedra, "seat") or bishop's throne is the chair or throne of a bishop. It is a symbol of the bishop's teaching authority in the Catholic Church and the Orthodox Church, and has in some sense remained such in the Anglican Communion and in Lutheran churches. Cathedra is the Latin word for a chair with armrests, and it appears in early Christian literature in the phrase "cathedrae apostolorum" indicating authority derived directly from the apostles;  its Roman connotations of authority reserved for the Emperor were later adopted by bishops after the 4th century. A church into which a bishop's official cathedra is installed is called a cathedral.
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 1666. As early as the 8th century, an ancient wooden chair overlaid with ivory plaques depicting the Labors of Hercules and some of the constellations http://rubens.anu.edu.au/raider4/europe.0602/germany/mainz/roemisches_germanisches_museum/ivories/cathedra_petri_9thc/IMGP0916.JPG was venerated as the episcopal chair of St. Peter. It is a Byzantine throne, made after St. Peter's time, with framed fragments of acacia wood encased in the oak carcass and reinforced with iron bands. 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 honor guard: St. Ambrose and St. Athanasius on the left, and St. John Chrysostom and St. Augustine on the right.
The Chair of St. Augustine represents one of the most ancient extant cathedrae in use. Named for the first Archbishop of Canterbury, St. Augustine of Canterbury, it is made of Purbeck Marble or Bethesda marble and dates to sometime between the 6th and 12th centuries. Those who argue for an older date suggest that it may have been used to crown the kings of Kent. Canterbury Cathedral, in which the cathedra is housed, maintains that the chair was once part of the furnishings of the shrine of St. Thomas Becket, since dismantled http://www.canterbury-cathedral.org/. Since antiquity, it is always 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.
The term ex cathedra, meaning "from the throne", is used to designate official pronouncements of the pope when he teaches the whole world. As a throne or armchair symbolizes the power to teach, the cathedra in this case refers to the teaching authority over the whole church rather than to a chair. According to Catholic dogma, the pope's statements ex cathedra are infallible in matters of faith and morals. In Anglican episcopal governance, episcopal teaching is conditioned by synodical governance, and so bishops cannot be said to speak ex cathedra in this way, although they may jocularly be said to do so.
The traditional position of the cathedra was in the apse, behind the high altar, which had been the position of the magistrate in the apse of the Roman basilica which provided the model type - and sometimes were adapted as the structures - for early Christian basilicas. In the Middle Ages, as altars came to be placed against the wall of the apse, the practice of placing the cathedra to one side (mostly left) became standard.
In the Roman Catholic Church since the Second Vatican Council, the altar is often free-standing, so that in cathedrals built or renovated after the reforms of Vatican II, the cathedra is often placed behind the altar, as in ancient Roman basilicas.
In Anglican practice, the cathedra tends to be placed to one side in the choir, although in more contemporary practice, it is commonly placed on the gospel side of the chancel (ie., to the left of the altar, as one looks at it from the front).
Eastern Orthodox and Eastern Catholic cathedrals will have a throne for the bishop in the apse behind the Holy Table (altar), with seats for the priests (Greek: synthranon)) arranged to either side of him. This location is referred to as the "High Place" and represents the presence of Christ presiding over the services, even when the bishop is not present. For this reason, the High Place often has an icon of Christ placed above the bishop's throne. The bishop ascends to the High Place only during the Divine Liturgy, at the Trisagion (at other times, if he sits in the sanctuary, a seat will be prepared for him on the side). For this reason, the Consecration of a bishop takes place at the Trisagion, so that he may ascend to the High Place for the first time as a bishop during the Liturgy at which he is Consecrated.
Another throne is provided for the bishop in the nave of the church:
An orlets, or "eagle rug" will usually be placed at both the High Place and the throne in the nave. The orletz also symbolized the bishop's authority, and he stands on it during services, even if he is not celebrating. An orletz is usually kept permanently on the Russian kafefra, even when the chair is removed.
Although an Hegumen (Abbot) does not have a cathedral, he may have a similar chair, likewise symbolic of his authority, reserved for him on the kliros of his monastery. The Hegumen's kathisma would be simpler than the one for the bishop, sometimes raised atop two steps, located to the side of the bishop's throne.