Bishop's throne in the cathedra of the Pope in the apse of St. John Lateran, the cathedral of Rome.

The Papal cathedra, which makes the Archbasilica the Cathedral of Rome, is located in the apse of St. John Lateran, the cathedral of Rome. The decorations are in cosmatesque style. The apse lined with mosaics and open to the air still preserves the memory of one of the most famous halls of the ancient palace, the "Triclinium" of Pope Leo III, which was the state banqueting hall. The existing structure is not ancient, but some portions of the original mosaics may have been preserved in the tripartite mosaic of its niche.

A cathedra (Latin, "chair", from Greek, καθέδρα kathédra, "seat") or bishop's throne is the seat of a bishop. It is a symbol of the bishop's teaching authority in the Catholic Church, the Orthodox Church, and in the Anglican Communion 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 apse is the semicircular or polygonal termination to the choir or aisles of a church. In relation to church architecture it is generally the name given to where the altar is placed or where the clergy are seated. The apse is separated from the main part of the church by the transept.

In architecture, the apse (from Latin absis: "arch, vault" from Greek ἀψίς apsis "arch"; sometimes written apsis; plural apsides) is a semicircular recess covered with a hemispherical vault or semi-dome, also known as an Exedra. In Romanesque, Byzantine and Gothic Christian abbey, cathedral and church architecture, the term is applied to a semi-circular or polygonal termination of the main building at the liturgical east end (where the altar is), regardless of the shape of the roof, which may be flat, sloping, domed, or hemispherical.

more on https://en.wikipedia.org/wiki/Archbasilica_of_St._John_Lateran , https://en.wikipedia.org/wiki/Apse