San Bernardo alle Terme

Stand still for a moment and look up. Above you, a single dome curves overhead like the inside of a great stone shell. It is ribbed with rows of sunken octagons that grow smaller as they climb towards the top. The light is soft and even. The street noise from outside fades quickly here, and the round walls seem to hold the quiet in. You are inside a church, but you are also inside something much older.

This is San Bernardo alle Terme, the Church of Saint Bernard at the Baths. The name tells you most of the story. The building you are standing in was not designed as a church at all. It began life as part of the Baths of Diocletian, the largest public bathing complex ever built in ancient Rome. The church simply moved into an existing Roman structure. That structure was a round tower on the corner of the baths' outer wall.

The baths were built at the very end of the third century and the start of the fourth, under the emperors Diocletian and Maximian. They covered an enormous area of this hill. Thousands of Romans could use them at once. There were hot rooms and cold pools, open courtyards for exercise, gardens, and halls for reading and conversation. For ordinary citizens, the baths were not a luxury. They were a daily social habit, a place to wash, meet friends, and do business.

This round building stood at one corner of the great outer enclosure. There was a matching rotunda at another corner of the same wall. Historians are not fully certain what these round halls were used for. They may have been meeting rooms, lecture spaces, or simply grand architectural anchors for the corners of the complex. What is clear is the quality of the building. Roman engineers put a solid masonry dome on top of it, and that dome is still standing over your head today.

After the fall of the Western Roman Empire, the baths slowly fell out of use. The aqueducts that fed them were cut, and without water, the great complex had no purpose. Over the following centuries, the structures were stripped, abandoned, and partly buried. This corner tower survived, though, mostly because its round shape and thick walls made it strong. For a long time it stood as a ruin at the edge of the city.

The change came at the end of the sixteenth century. In 1598, a noblewoman named Caterina Sforza of the Santa Fiora family paid for the tower to become a church. She gave it to a community of Cistercian monks from France. The Cistercians are a strict branch of the Benedictine tradition, known for simple living and hard work. That explains the dedication. Saint Bernard of Clairvaux was the most famous Cistercian of the Middle Ages, a powerful preacher of the twelfth century.

Now look again at the dome, and compare it in your mind with the Pantheon on the other side of central Rome. The resemblance is not an accident. Both are round Roman halls topped by a coffered dome. Coffers are the sunken panels you can see, cut into the surface in a repeating pattern. They make the dome lighter, and they also give it rhythm and depth. Here the coffers are eight-sided, and they shrink row by row as they rise.

Here is something many visitors miss. The building has a quiet double life. From inside, it feels like a calm Renaissance church. From outside, if you walk around it, you can still see the curve of the Roman wall and the solid brickwork of the original tower. The new entrance and facade were added at the front. But the body of the building is still ancient Rome, put to a new use.

Now turn your attention to the niches around the walls. Each one holds a large white statue of a saint. These figures are made of stucco, a kind of plaster that can be modelled and polished to look like marble. They are the work of the sculptor Camillo Mariani, from the years when the church was being fitted out. Look closely and you can see how expressive they are. Heavy drapery, turning bodies, faces caught in thought or prayer.

The second surprise is in the floor and walls, among the tombs. The German painter Johann Friedrich Overbeck is buried in this church. He was a leader of a group of nineteenth century German artists, often called the Nazarenes. They lived in Rome and tried to bring a simple, devout spirit back into painting, inspired by early Italian masters. Overbeck spent most of his life in this city. It is fitting that he rests in a building where so many layers of Roman history meet.

When you step back outside, notice where you are. This is a busy crossroads of churches and fountains. Nearby stands Santa Maria della Vittoria, home to Bernini's famous sculpture of Saint Teresa in ecstasy. Across the square is the large Fountain of Moses, built to celebrate the return of fresh water to this hill. That return of water matters here. The same hill that lost its baths when the aqueducts were cut came back to life when new water arrived centuries later.

A short walk away is another church built inside the same Roman baths. Santa Maria degli Angeli was shaped from the baths' central hall, with designs connected to Michelangelo. Visiting both gives you a sense of how huge the original complex was. One Roman building became two churches, a museum, streets, and squares. It is a good reminder that much of Rome is built inside and on top of earlier Rome.

This church is small compared with the great basilicas of the city. That is part of its charm. It is a place where you can stand at the centre, turn slowly, and take in the whole space with one look. There is no long nave to walk down. The round plan pulls your eyes upward and inward. Many people find it one of the calmest interiors in this part of the city.

Before you leave, take one last look at the dome. Follow the rows of octagons from the bottom edge up to the top. Those lines were set out by Roman builders around seventeen centuries ago, and later generations decided to keep them. As you walk back into the street, listen for the traffic returning, and feel how quickly the quiet slips away behind you.