St. Peter's Basilica

This is the largest church in the world, and the Vatican will not let you forget it. On the floor of the nave, there are brass markers showing where every other major church in the world would end if you placed it inside this one. St Paul's Cathedral in London? It fits with room to spare. The building is two hundred and twenty metres long, covers twenty-three thousand square metres, and can hold over twenty thousand people. Bernini's colonnade out front has two hundred and eighty-four columns and eighty-eight pilasters arranged in four rows. It took eleven years.

The building sits directly over what tradition — and modern archaeology — identifies as the burial site of Saint Peter, the first pope. In the 1940s, Pope Pius XII authorised excavations beneath the basilica, and archaeologists found a Roman necropolis that had been sealed since the fourth century. They found bones wrapped in purple and gold cloth in a niche marked with early Christian graffiti. Pope Paul VI later announced these were the bones of Saint Peter, though the identification remains debated.

Michelangelo designed the dome when he was seventy-one years old. He never saw it finished — he died in 1564, and it was completed in 1590 by Giacomo della Porta. It is one hundred and thirty-six metres high from floor to lantern top, and climbing the five hundred and fifty-one steps to the viewing platform is one of those experiences that starts exciting and becomes progressively more claustrophobic as the walls curve inward. The dome weighs approximately fourteen thousand tonnes.

The Pieta — Michelangelo's sculpture of Mary holding the dead Christ — is behind bulletproof glass now, ever since a man attacked it with a hammer in 1972, breaking off Mary's arm and nose. It is the only work Michelangelo ever signed. He did it across Mary's sash after overhearing visitors credit the sculpture to another artist. He was twenty-four when he carved it. He never signed another work again.