Michelangelo's last great work, the Dome of St. Peter's, has a diameter of around 43 meters; it sits on four great arches that stand on four massive piers, each with a perimeter of 71 meters. When Michelangelo died, the drum was already in place with its 16 windows.

Giacomo della Porta finished the work with the construction of the actual dome, raising it 10 meters so it now rests 136 meters above floor level. This deviation from the original design caused it to lose some of the round shape Michelangelo had planned. The mosaics were completed later, following designs by Cavalier d'Arpino.