The apse is at the end of the central nave. In the center is the Altar of the Chair of Peter, a masterpiece which is unmistakably the work of Gian Lorenzo Bernini (1598-1659).
Every year on February 22, the Church celebrates the feast of the Chair of St. Peter, to commemorate St. Peter's teaching in Rome. Already in the second half of the 18th century an ancient wooden chair inlaid with ivory was venerated and traditionally held to be the Episcopal chair on which St. Peter sat as he instructed the faithful of Rome. In fact, it is a throne in which fragments of acacia wood are visible, which could be part of the chair of St. Peter, encased in oak and reinforced with iron bands. Several rings facilitated its transportation during processions. Pope Alexander VII commissioned Bernini to build a sumptuous monument which would give prominence to this ancient wooden chair. Bernini built a throne in gilded bronze, richly ornamented with bas-reliefs in which the chair was enclosed: two pieces of furniture, one within the other. On January 17, 1666 it was solemnly set above the altar.
The base of the altar is made of black and white marble from Aquitaine and red jasper from Sicily. Four gigantic statues (about 5 m. tall) in gilded bronze surround the Chair which looks almost as if it were suspended amidst the clouds. The two outer statues are figures of two Doctors of the Latin Church: St. Ambrose and St. Augustine; the two inner statues, with bare heads, are of two Doctors of the Greek Church: St. Athanasius and St. John Chrysostom. These saints represent the catholicity of the Church and at the same time, the consistency of the theologians' teaching with the doctrine of the Apostles.
Above the Chair are two angels bearing the tiara and keys, symbols of the Roman pontiff's authority. On the Chair, are three bas-reliefs picked out in gold, which refer to the same number of Gospel episodes: the Consignment of the keys, Feed my sheep, and the Washing of the feet.
The whole composition is crowned by the fantastic gilt and stucco Gloria peopled by a host of angels among rays of light and gigantic billowing clouds. In their midst is the precious window of Bohemian glass, divided into twelve sections as a tribute to the Twelve Apostles; a brilliant dove stands out against it, the symbol of the Holy Spirit, the soul of the Church which he never ceases to help and to guide. Vanvitelli decorated the vault with gilded stucco. In the three medallions are portrayed: the Consignment of the Keys, the Crucifixion of St. Peter and the Beheading of St. Paul.
 The Cathedra Petri area |
 The Gloria above the Cathedra |
 Sts. Ambrose (left) and Anthanasius |
 Sts. John Chrysostom and Augustine (right) |
From: 'Guide to Saint Peter's Basilica'
This structure is a brilliant creation by Bernini, designed to display the chair on which, according to ancient tradition, St. Peter sat and taught Roman Christians. Pope Alexander VII had the ivory-covered chair put into the gigantic bronze cathedra, with the statues of the Doctors of the Church, St. Ambrose and St. Augustine of the Roman Church and St. Athanasius and St. John Chrysostom of the Greek Church. The religious significance is extremely clear. The Doctors of the Church were always consistent with Peter's teachings as they expounded theological doctrine.
The gospel does not change because the Holy Spirit, portrayed as a dove flies along the span of the centuries, assisting and accompanying its church. The chair or cathedra of Peter symbolizes the perpetual continuity of the doctrine and its promise of infallibility. It triumphed over all heresies throughout the centuries.
The fine alabaster window, surrounded by golden clouds and angels flying between rays of light, casts a mystical warmth through the basilica, especially in the afternoon. It is divided into twelve sections, in homage to the twelve Apostles who carried the words of the Gospel throughout the world.