The great dome of St Peter's Basilica was completed by Giacomo della Porta in 1590, the fifth year of the pontificate of Sixtus V (r. 1585-90), as the Latin inscription, at the base of the lantern, proclaims.
The decoration of the interior of the cupola began three years later, in 1593. The mosaics are divided into six concentric rings. Starting at the base of the cupola (above the sixteen windows), the mosaics depict:
1. 16 pope-saints buried in the basilica.
2. Figures of Christ, Virgin Mary, St. Paul, St. John the Baptist and the 12 Apostles.
3. Angels bearing the instruments of Christ's Passion.
4. Heads of cherubim and seraphim in circular medallions.
5. Angels, the custodians of St. Peter's tomb.
6. Heads of angels.
The long inscription (in letters 2 metres high), at the base of the dome, reads: TV ES PETRVS ET SVPER HANC PETRAM AEDIFICABO ECCLESIAM MEAM ET TIBI DABO CLAVES REGNI CAELORVM (Thou art Peter, and upon this rock I will build my church. And I will give unto thee the keys of the kingdom of heaven, Matthew: 16:18, KJV).
The shorter inscription, which runs round the base of the lantern, reads: S PETRI GLORIAE SIXTVS PP V A M D XC PONTIF V (Pope Sixtus the Fifth to the glory of St Peter, in the year 1590, the fifth of his pontificate).
In addition to the inscription to Sixtus V, there are further references to the pope on the exterior of dome. They take the form of a series of lions' heads flanked by bunches of pears, part of the pope's armorial bearings. (His family name was Peretti-Montalto and pera is the Italian word for pear.)
My name is David Lown and I am an art historian from Cambridge, England. Since 2001 I have lived in Italy, where I run private walking tours of Rome.
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