Sant'Agnese in Agone

Stand still for a moment and listen. Water pours from Bernini's fountain behind you. Street painters scrape their easels across the paving stones. Somewhere a waiter calls an order. And above all this noise, a pale stone facade curves gently inward, as if the building were taking a slow breath. This is Sant'Agnese in Agone, the church that faces the long oval of Piazza Navona.

That oval shape is your first clue to what lies under your feet. In the first century, the Emperor Domitian built a stadium here for athletic contests. The Greek word for such contests was agon, or in plural, agones. Over the centuries, Romans built houses directly into the old stands, and the arena became the square. The name of the church carries that ancient sports ground inside it — Saint Agnes at the games.

The saint herself was a young Roman girl, a Christian martyr from the early fourth century or a little before. Tradition places her suffering right here, in the arches of the stadium, where the poor and the condemned once gathered. Legend has it that she was stripped and exposed to the crowd, and that her hair grew miraculously long to cover her body. It is a story, not a record. But it gave this spot its sacred meaning for well over a thousand years.

The church you see now belongs to a later and much more confident age. In the middle of the seventeenth century, Pope Innocent X decided to rebuild it. He came from the Pamphilj family, and their family palace stands right next door, to your left as you face the church. This was not only an act of devotion. The Pope wanted the whole square to become a stage for his family's name, with the church as its centrepiece.

Work began in 1652 under the architects Girolamo Rainaldi and his son Carlo. Within about a year, the Pope replaced them with Francesco Borromini, one of the most inventive architects of the Baroque — the dramatic, theatrical style that swept through Rome in that century. Borromini changed the plan in a bold way. He pulled the centre of the facade backward into a concave curve, so the dome could come forward and be seen from the square.

Look at that effect now. On a narrow street, a dome is often hidden behind a flat front wall. Here, the curve opens like a pair of arms, and the drum and dome rise clearly above it. On either side, two bell towers frame the composition. The whole front reads as one movement, from the towers down into the hollow and back up into the dome. It is architecture that wants you to stand back and take it in.

Borromini did not finish the job. After the death of Innocent X in 1655, support for the project weakened, and Borromini left the work a couple of years later. Other architects, including Carlo Rainaldi again, completed the building, and they altered several of his details. So what you see is a shared creation. The main idea of the curved front is Borromini's, but many finishing touches belong to other hands.

Now turn around and look at the fountain. This is the Fountain of the Four Rivers, designed by Gian Lorenzo Bernini, Borromini's great rival. Four giant figures represent rivers from four continents — the Danube, the Ganges, the Nile, and the Rio de la Plata. The Nile has its head covered with a cloth. One figure raises an arm, as if to block something from view. Here begins one of Rome's favourite stories.

Locals love to say that Bernini mocked his rival in stone. According to the popular tale, the river god raises his hand because he fears the church will fall on him, and the Nile hides his face so he does not have to look at it. It is a wonderful story — and it cannot be true. The fountain was completed in 1651, before Borromini began work on the facade. The covered head of the Nile most likely refers to something else entirely: in Bernini's day, nobody in Europe knew where the river's source was.

There is a matching legend on the church itself. High on the facade stands a statue of Saint Agnes. Some guides claim she places her hand on her heart to promise that the building is safe and will not collapse. Again, enjoy it as Roman humour, not history. The real rivalry between the two artists was intense and well documented. The jokes in stone were added later by the people who loved to watch them compete.

If the doors are open, step inside. The interior is surprisingly compact. The plan is based on a Greek cross, a cross with four arms of almost equal length, so everything gathers under the central dome. Marble in white, grey, and warm colours lines the walls. Large carved altarpieces stand in the niches instead of painted ones. Look up into the dome, and in the four curved corners below it you will see paintings by Giovanni Battista Gaulli, known as Baciccio, showing the Virtues.

Here is a detail many visitors miss. The church keeps a relic believed to be the skull of Saint Agnes, displayed in a small chapel. Her body rests in a different church, Sant'Agnese fuori le Mura, on the edge of the city. And below the floor, in the lower level, there are remains of Domitian's stadium and older chapels. One of them holds a marble relief by the sculptor Alessandro Algardi showing the miracle of Agnes's hair. Access to these lower rooms is not always possible.

Near the entrance, look for the tomb of Innocent X, the Pope who began all of this. He lies in the church that was meant to glorify his family, just steps from the palace where they lived. Outside, the square continues as it has for centuries. In the seventeenth and eighteenth centuries, Romans even flooded parts of the piazza on hot summer weekends, and carriages splashed through the water for fun.

Before you move on, take one last look at the curve of the facade. Notice how the light falls differently across it as the day changes, bright on the towers and softer in the hollow. Under your feet lies an ancient racetrack. In front of you stands a Baroque church built on a martyr's story. Behind you, a rival's fountain keeps running. As you walk away along the long oval of the square, you are walking the lines of Domitian's stadium.