Piazza Navona

The elongated shape of the square gives away its origins: you are standing on the stadium that the emperor Domitian built around AD 86 for athletic contests. The houses were raised on top of the old stands, which is why the square still follows the outline of the track.

1The rivalry that never was

In the centre, Bernini's Fountain of the Four Rivers (1651) represents the Danube, the Ganges, the Nile and the Río de la Plata. Opposite rises the church of Sant'Agnese in Agone, with a façade by Francesco Borromini, Bernini's great rival.

Tradition has it that the Río de la Plata raises his hand to shield himself from a façade that, according to Bernini, was about to collapse, and that the Nile covers his head so as not to see it.

It's a wonderful story, but the dates won't have it: the fountain was finished in 1651 and Borromini did not take over the façade until 1653. The Nile's head is veiled for a more learned reason: in the 17th century nobody knew where its source lay.

2The saint's hair and the flooded square

The church honours St Agnes, a Roman martyr. According to her legend, she was exposed naked here, under the arches of the stadium, and her hair miraculously grew to cover her. And another oddity, this one documented: from 1652 to 1866, on August weekends, the drains were blocked and the square was flooded so that nobles' carriages could splash through the water while the crowds looked on.

3What to look for

• The Río de la Plata, with his arm raised, and the Nile with his face covered.
• The dove with an olive branch on top of the obelisk, emblem of the Pamphili family of Pope Innocent X.
• The curve at the north end, which follows the line of the ancient track.