St. Peter's, the majestic basilica in the Vatican, is the largest church in the world. To many, it is the most impressive, richly detailed, and artistically expressive in Europe. Construction of St. Peter's took place between the 14th and 16th centuries. Old St. Peter's was at that time more than 1100 years old and showing signs of age. Pope Julius II entrusted Donato Bramante with the complete rebuilding of St. Peter's to a new design. Bramante's plan was based on a Greek cross--one with equal arms--featuring a large central dome surrounded by lesser domes.


Although he professed to know little about architecture, Michelangelo is said to have inspected St. Peter's one day. As he circled the construction site he observed that the workmen pouring the foundations and piers were not following accepted practice of using one portion of cement to three or four of sand, but were mixing ten or twelve portions of sand to each of cement. In addition, the concrete walls were hollow and being filled with rubble from the old basilica and other debris. The structure might appear solid but would never support so massive a load. Michelangelo reported his findings to the architect, Bramante, but was rebuffed as a troublemaker. Later, some of Bramante's work would have to be torn down and replaced or reinforced several times, vindicating Michelangelo.

When Bramante died in 1514, the structure was not complete. For several years Popes and architects succeeded each other with little effect on St. Peter's until 1547, when Michelangelo was appointed chief architect. Michelangelo regarded the work on St. Peter's as his most important commission, and he remained in the position until his death at age 89. Michelangelo's dome was an aesthetic and structural triumph. Designed as two shells, it would be higher, lighter, and more graceful than the single shell domes proposed by Bramante and his successors.