Below is the great dome that soars above the altar and the baldacchino, sumptuously embellished with mosaic and stucco ornaments. It is supported by four structural piers with a perimeter of 71 m. and a height of 120 m. from the ground to the roof of the lantern.
The giant letters on a gold background, from St. Veronica to St. Helen, say "Hinc una fides mundo refulgent" (From here a single faith shines throughout the world); and from St. Longinus to St. Andrew: "Hinc sacerdotii unitas exoritur" (From here is born the unity of the priesthood).
In the four spandrels which link the square piers and the circular drum, the four Evangelists are portrayed in medallions with a diameter of 8.5 m.: Matthew with the ox, Mark with the lion, Luke with the angel and John with the eagle.
The dome is decorated with mosaics, from originals by Francesco Trevisani da Capodistria. In the spandrels are portrayed the races of the four continents which became Christian: Europe, Asia, Africa, America. In the lunettes are various baptismal scenes: Jesus baptizes Peter, St. Peter baptizes the Centurion Cornelius, St. Philip baptizes the Eunuch of Queen Candace, St. Silvester baptizes Constantine, and several symbols of baptism: Moses causes the water to spring from the rock, Noah prays before the rainbow of the Covenan
From looking at the ceilings, we then proceed to look at more altars and monuments within St Peter's Basilica...