Ponte Sisto site features

It is low, pale and short, and you are across it in ninety seconds. Four travertine arches carry a flat roadway between two riverbanks, with nothing on it — no statues, no lamps on columns, no traffic. After the Tiber's other bridges, the plainness is the first thing you notice.

Then you see the hole. Above the central pier, in the spandrel between the two middle arches, is a perfectly circular opening straight through the masonry, big enough to put a person through, with the river visible on the other side of it. It looks decorative and it is not.

Five marble shields are set along the parapets — papal arms, worn flat by weather and hands.

The view downstream is the one on the postcards. The river runs away between plane trees on both embankments, and beyond the rooftops the dome of Saint Peter's stands up against the sky.

At the Trastevere end the bridge opens into a small square with a fountain and a wall of bars, and in the evening the crossing fills with people going one way — into Trastevere — and buskers set up in the middle of the span.

The oculus

The circular opening at the centre, lightening the masonry of the central spandrel, erected to diminish the river's pressure on the bridge in case of flood. Visible from the embankment, not from the deck.

Four travertine arches

On the reused foundations of the Roman Pons Aurelius, dated by Turismo Roma to 12 BC and built perhaps by Agrippa.

Five papal coats of arms

In marble, along the bridge.

The Platina inscriptions

An elegant Latin inscription composed by the humanist Bartolomeo Platina in honour of Sixtus IV. What is on the bridge now are copies — the originals removed in the 1990s after continued vandalism, says the reference work; removed to preserve them from the ravages of time and transcribed on the new parapets facing via Giulia, says Turismo Roma.

The view of the dome

Turismo Roma describes a postcard backdrop in which the Dome of Saint Peter's can be made out.

The missing iron walkways

Added in 1877 by Angelo Vescovali, in soft iron and cast iron, and removed in 2000 by Gaetano Miarelli Mariani.

The unsettled architect

The reference work says Baccio Pontelli. Turismo Roma says the attribution has fallen and the author is unresolved.