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The widest masonry dome in Europe is precisely as high as it is wide: 43.3 m (142 ft). Its airy, coffered space, cleverly shot through with a shaft of sunlight from the oculus, is what lends the Pantheon an ethereal air.

The bold, 8.3 m-diameter (27-ft) hole at the dome’s centre provides light and structural support: the tension around its ring helps hold the weight of the dome.

The triangular pediment is supported by 16 pink and grey granite columns, all original save the three on the left (17th-century copies).

The massive bronze doors are technically original, but were so extensively renovated under Pius IV (1653) they have been practically recast.

The 6.2-m (20-ft) thick walls incorporate built-in brick arches to help distribute the weight downwards, relieving the stress of the heavy roof.

Two of Italy’s kings are honoured by simple tombs. Vittorio Emanuele II (1861–78) unified Italy and became its first king. His son, Umberto I, was assassinated in 1900.

Raphael, darling of the Roman Renaissance art world but dead at 37, rests in a plain, ancient stone sarcophagus. Poet Bembo’s Latin epitaph translates as: “Here lies Raphael, whom Nature feared would outdo her while alive, but now that he is gone fears she, too, will die.” Other artists buried here include Baldassare Peruzzi.

Giacomo della Porta designed this stoop; Leonardo Sormani carved it in 1575. The Egyptian obelisk of Rameses II was added in 1711.

Red porphyry, giallo antico, and other ancient marbles grace the interior. More than half the polychrome panels cladding the walls are original, the rest careful reproductions, as is the floor.

Of the Pantheon’s old neighbour, all that remains are an elaborate cornice and fluted columns against the Pantheon’s rear wall.