Central dome of St. Peter's in the Vatican City, Rome. View from the roof of St. Peter's.

St. Peter's is a church in the Renaissance style located in the Vatican City west of the River Tiber and near the Janiculum Hill and Hadrian's Mausoleum. Its central dome dominates the skyline of Rome.
The dome of St. Peter's rises to a total height of 136.57 metres (448.1 ft) from the floor of the basilica to the top of the external cross. It is the tallest dome in the world.[38] Its internal diameter is 41.47 metres (136.1 ft), slightly smaller than two of the three other huge domes that preceded it, those of the Pantheon of Ancient Rome, 43.3 metres (142 ft), and Florence Cathedral of the Early Renaissance, 44 metres (144 ft). It has a greater diameter by approximately 30 feet (9.1 m) than Constantinople's 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. Giacomo della Porta and Domenico Fontana brought the dome to completion in 1590, the last year of the reign of Sixtus V. 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.

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