It’s the world’s largest Basilica of Christianity, nested into the heart of the Vatican city. The original basilica was commissioned by the emperor Constantine and built around 349 on the site where St Peter is said to have been buried between AD 64 and 67. But like many medieval churches, it eventually fell into disrepair and it wasn’t until the mid-15th century that efforts were made to restore it, first by Pope Nicholas V and then, rather more successfully, by Julius II. In 1506 Bramante came up with a design for a basilica based on a Greek-cross plan, with four equal arms and a huge central dome. But on Bramante’s death in 1514, construction work ground to a halt as architects, including Raphael and Antonio da Sangallo, tried to modify his original plans. Little progress was made and it wasn’t until Michelangelo took over in 1547 at the age of 72 that the situation changed. Michelangelo simplified Bramante’s plans and drew up designs for what was to become his greatest architectural achievement, the dome. He never lived to see it built, though, and it was left to Giacomo della Porta and Domenico Fontana to finish it in 1590. With the dome in place, Carlo Maderno inherited the project in 1605. He designed the monumental facade and lengthened the nave towards the piazza. A monument to centuries of artistic genius, it contains some spectacular works of art, including three of Italy’s most celebrated masterpieces: Michelangelo’s Pietà , his breathtaking dome, and Bernini’s baldachin (canopy) over the papal altar.