"Simple, erect, severe, austere, sublime—
Shrine of all saints and temple of all gods,
From Jove to Jesus—spared and blest by time"Lord Byron, Childe Harold's Pilgrimage (IV.146)
The great oculus of the Pantheon is twenty-nine feet across and provides the only source of light. Just as there are seven niches around the floor, which may have held images of the seven planetary deities (cosmocratores), so there are seven rings on the vault: the five coffered rings and the plain ring surrounding the oculus, which is the seventh circle. Within this circle is another, as both the diameter of the rotunda and its height are the same. In this is a representation of the universe itself, in microcosm. The thickness of the dome diminishes as it approaches the oculus, from almost twenty feet at the base to five feet at the top. Weight was reduced further by the lacunar coffering, which once held gilded bronze rosettes, and the use of progressively lighter aggregate in the concrete until, at the top, volcanic pumice was used.
Built by Agrippa, the Pantheon was destroyed in the fire of AD 80, restored, burned again thirty years later, and was completely rebuilt between AD 118 and AD 128 by Hadrian, who retained the original inscription on the façade. The triangular pediment is exceptionally high to hide the rotunda; the tympanum, now empty, originally contained a bronze eagle.
The Pantheon escaped the depredations of the barbarians and was presented in AD 609 by the Byzantine emperor Phocas to the pope, who rededicated the temple as a church. Of all the buildings in ancient Rome, the Pantheon is the best preserved, its masonry dome still the largest ever built and one of the greatest achievements of Roman engineering.
"This Pope was Boniface, fourth Bishop of Rome after Gregory, who persuaded the Emperor Phocas to give the Christian Church the Rome temple anciently known as the Pantheon, in which stood images of all the gods. After solemn purification, Boniface consecrated it as the Church of the Holy Mother of God and all Christian Martyrs; and once its horde of devils had been cast out, it became a memorial to the Company of Saints."
Bede, Ecclesiastical History (II.4)
