Just west of San Luigi dei Francesi lies Piazza Navona, Rome’s most famous square. Lined with cafés and restaurants, and often thronged with tourists, street artists and pigeons, it is as picturesque – and as vibrant, day and night – as any piazza in Italy. It takes its shape from the first-century-AD Stadium of Domitian, the principal venue of the athletic events and later chariot races that took place in the Campus Martius. Until the mid-fifteenth century the ruins of the arena were still here, overgrown and disused, but the square was given a facelift in the mid-seventeenth century by Pope Innocent X, who built most of the grandiose palaces that surround it and commissioned Borromini to design the facade of the church of Sant’Agnese in Agone on the piazza’s western side. The story goes that the 13-year-old St Agnes was stripped naked before the crowds in the stadium as punishment for refusing to marry, whereupon she miraculously grew hair to cover herself. The church, typically squeezed into the tightest of spaces by Borromini, is supposedly built on the spot where it all happened.Opposite, the Fontana dei Quattro Fiumi, one of three that punctuate the square, is a masterpiece by Bernini, Borromini’s arch-rival, and it’s said that all the figures are shielding their eyes in horror from Borromini’s church facade (Bernini was disdainful of the less successful Borromini, and their rivalry is well documented), but the fountain had actually been completed before the facade was begun. The grand complexity of rock, which represents the four great rivers of the world, is topped with an Egyptian obelisk, brought here by Pope Innocent X from the Circus of Maxentius.