St. Peter's Basilica site features

You cross the piazza, pass security, climb a few steps, and the scale stops being describable. The doorway is ordinary enough that people walk through it talking. Then the interior opens: a nave in three huge bays under a barrel vault that the reference work calls the highest of any church, running away from you further than it looks, because everything in it is oversized and the eye has nothing familiar to measure against.

The trick is that nothing is the size it appears. The putti holding the holy-water stoups are the size of adults. The gold letters of the inscription running round the base of the dome are taller than a person. There are brass markers set into the nave floor showing where the next-largest churches in the world would end if they were laid inside this one, and the nearest of them is a long way short of the door.

At the crossing, Bernini's baldachin. A canopy of dark, almost black bronze over the papal altar, carried on four twisted columns that corkscrew upward the height of a building, with bronze drapery and foliage worked over them. It stands directly beneath the dome, and it is the one object big enough to hold that space without being swallowed by it.

Above it, Michelangelo's dome. Coffered, ribbed, climbing to a lantern so far up that the daylight coming through reads as a separate weather. The mosaic figures ringed around its base look small and are not.

Off to the right of the entrance, behind glass, the Pietà. Michelangelo carved it at twenty-four: the dead Christ across his mother's lap, polished to a shine the rest of the building does not have. It is small, and it is the thing most people came for.

Michelangelo's dome

Designed by him and completed by Della Porta and Fontana in 1588-89. The climb is separately ticketed and keeps its own, earlier hours.

The Pietà

Michelangelo, 1498-99, behind glass to the right of the entrance. The only work he signed.

Bernini's baldachin

The bronze canopy over the papal altar, carried on four twisted columns, worked with the Barberini bee — Urban VIII's family emblem.

Maderno's facade

115 metres long, seventeenth-century, and the reason Michelangelo's dome vanishes from view as you cross the piazza.

The nave

Three bays, piers carrying a barrel vault the reference work calls the highest of any church, in the largest church in the world by interior measure.

Constantine's basilica

The church that stood here from around 320, which Turismo Roma notes was comparable in size to the present one.