Castel Sant'Angelo site features

It is a drum on a box, and from the bridge it reads as one solid mass. A low square base carries a huge brick cylinder, and on top of that sits a smaller tier, and on top of that a dark bronze angel with its wings up, sheathing a sword.

The approach is across a bridge lined with angels. Ten marble figures, five a side, each carrying something — a column, a crown of thorns, a lance — all leaning slightly into the wind, all facing the castle.

Round the base is a dry moat and four arrowhead bastions, grass-floored, which is where the building stops looking like a tomb and starts looking like artillery.

Inside, you climb a ramp that spirals through the solid core. It is wide, brick-walled, lit at intervals, and it rises continuously — built for a funeral procession rather than for stairs.

Then the rooms turn into a palace. Painted ceilings, grotesques, cupids and griffins on white grounds, a hall with frescoed walls — and off them, lower down, small stone chambers with no windows.

At the top the terrace runs right round. The Tiber bends away below, the bridge's angels are foreshortened into a line, and the dome of Saint Peter's is close enough to look at rather than towards.

The Passetto di Borgo

The covered corridor to the Vatican, built under Niccolò III Orsini, which carried Alexander VI out in 1494 and Clement VII in 1527.

The burial chamber, and the clamps

At the centre of the mausoleum, once faced in precious polychrome marble; the clamps that held the slabs are still visible.

The terraces

Turismo Roma: one of the most striking panoramas of the city, above all at sunset.

Bernini's angels

Ten marble angels placed along the bridge by Clement IX between 1667 and 1669, by Bernini and his workshop — the first two, by Bernini himself, are in Sant'Andrea delle Fratte. The reference work notes they hold instruments of the Passion of Christ.

The Sala di Apollo

Grotesques by Perin del Vaga, drawn from the Domus Aurea: cupids, griffins, satyrs and tritons.

Sangallo's bastions

Four pentagonal bastions and the moat, built for Alexander VI by Antonio da Sangallo the Elder.

The Sammalò

A cell the condemned was lowered into from above, with barely room to crouch — unable to stand or lie down.

The famous prisoners

Beatrice Cenci, Benvenuto Cellini, Cagliostro and Giordano Bruno.

Tosca

Puccini set the opera here: Cavaradossi shot in the courtyard, and Tosca throwing herself from the ramparts.