Photos

Dome- successive designs and final solution

The dome of St. Peter's rises to a total height of 136.57 m (448.06 ft) from the floor of the basilica to the top of the external cross. It is the tallest dome in the world.[24] Its internal diameter is 41.47 metres (136.06 ft), being just slightly smaller than two of the three other huge domes that preceded it, those of the Pantheon of Ancient Rome and Florence Cathedral of the Early Renaissance. It has a greater diamater by approximately 30 feet than that of the third great dome, Constantinople's Byzantine church of Hagia Sophia church, completed in 537. It was to the domes of the Pantheon and Florence duomo that the architects of St. Peter's looked for solutions as to how to go about building what was conceived, from the outset, as the greatest dome of Christendom.

Completion
The dome was brought to completion by Giacomo della Porta and Fontana.

Giacomo della Porta and Fontana brought the dome to a completion in 1590, the last year of the reign of Sixtus V. His successor, Gregory XIV, saw Fontana complete the lantern and had an inscription to the honour of Sixtus V placed around its inner opening. The next pope, Clement III, had the cross raised into place, an event which took all day, and was accompanied by the ringing of the bells of all the city's churches. In the arms of the cross are set two lead caskets, one containing a fragment of the True Cross and a relic of St. Andrew and the other containing medallions of the Holy Lamb.[19]

In the mid-18th century, cracks appeared in the dome, so four iron chains were installed between the two shells to bind it, like the rings that keep a barrel from bursting. As many as ten chains have been installed at various times, the earliest possibly planned by Michelangelo himself as a precaution, as Brunelleschi did at Florence Cathedral.

Around the inside of the dome is written, in letters 2 metres (6.5 ft) high: