Santa Maria del Popolo

Stand for a moment just inside the old city gate. Behind you, traffic hums along the edge of a wide oval square. In front of you, an obelisk rises against the sky. And here, almost pressed against the city wall, is a modest church front of pale stone. It looks quiet, almost plain. Push open the door, though, and the noise of the piazza falls away. The air turns cool. Somewhere a candle flickers. You are standing in one of the richest small churches in Rome.

This is Santa Maria del Popolo, the Church of Saint Mary of the People. For centuries, travellers arriving from the north entered Rome through the gate beside you. It stood at the end of the Via Flaminia, the ancient Roman road from the Adriatic coast. Pilgrims, merchants, and artists all passed this spot. So this church was often the very first thing they saw. In a sense, it was Rome's front door... and the popes decorated it like one.

The church begins with a ghost story. Legend has it that the emperor Nero was buried near here. Locals said his restless spirit haunted a walnut tree on this spot, and that demons gathered in its branches. According to the popular tale, Pope Paschal II had a dream around the year 1099. He ordered the tree cut down and built a chapel to the Virgin Mary in its place. Whether you believe it or not, the story stayed with the church for centuries.

The building you see today is much younger than that first chapel. It was rebuilt in the 1470s under Pope Sixtus IV, a member of the powerful della Rovere family. This was the early Renaissance, when Roman builders were rediscovering the clean lines of ancient architecture. Look at the facade on your way out. It is calm and balanced, with simple pilasters and a triangular top. Later, in the seventeenth century, the great sculptor Gian Lorenzo Bernini made changes to the front and the interior.

Now walk up the nave toward the main altar. Look for the chapel just to the left of it. This is the Cerasi Chapel, and it holds two paintings by Caravaggio. He painted them at the very start of the seventeenth century, when he was the most talked-about artist in Rome. Many visitors come here for these two canvases alone. They hang on the side walls, facing each other, so you have to turn your head to see them properly.

On one side is the Conversion of Saint Paul. Here is the first surprise. The biggest thing in the painting is not the saint. It is a horse. Paul lies on his back on the ground, arms open, eyes closed, blinded by a light we cannot see. The horse lifts one hoof carefully, so as not to step on him. An old groom holds the bridle. There is no crowd, no sky, no angel. Just a man, an animal, and a sudden shaft of light.

On the opposite wall is the Crucifixion of Saint Peter. Tradition says Peter asked to be crucified upside down, because he felt unworthy to die like Christ. Caravaggio shows the moment the cross is being raised. Three workmen strain under the weight. One crouches with his back to us, and the dirty soles of his feet face the viewer. Peter, old and heavy, turns his head and looks past them. Between the two Caravaggios, above the altar, hangs a bright Assumption of the Virgin by Annibale Carracci, his great rival.

Turn back down the church now and find the second chapel on the left side as you face the altar. This is the Chigi Chapel. It was designed by Raphael for Agostino Chigi, a banker so rich he lent money to popes. Raphael planned the whole space as a single work of art, from the floor to the dome. But both men died before it was finished. More than a century later, another member of the Chigi family became Pope Alexander VII, and he asked Bernini to complete it.

Look up into the dome. A mosaic shows God the Father at the centre, his arms raised. Around him are panels with the planets, each guided by an angel. It is a picture of the heavens as Renaissance thinkers imagined them. Then look at the walls. The two tombs are shaped like tall, narrow pyramids. That was an unusual choice for a Christian chapel. It points back to ancient Rome, where a few wealthy citizens built pyramid tombs of their own.

Now the second surprise. Look down at the floor. Set into the marble is a winged skeleton, made of coloured stone inlay. It holds the Chigi family coat of arms. It is a reminder that death comes for everyone, even the richest banker in Rome. In the corners, Bernini added marble statues. One shows the prophet Habakkuk, and an angel who grabs him by the hair. Across the chapel sits Daniel, praying beside a lion. The two figures seem to be part of the same story, reaching across the room.

This chapel also has a modern fame. Readers of Dan Brown's thriller Angels and Demons may recognise it, because the novel uses the Chigi Chapel as one of its settings. So do not be surprised if a few visitors are hunting for clues. The real history is strange enough on its own. Behind the main altar, the vault of the choir is painted with frescoes by Pinturicchio, an Umbrian artist who worked for several popes. Their soft colours are easy to miss, so take a moment to look up.

One more story belongs to this place. The church was served by Augustinian friars, who lived in the convent next door. In 1510 or 1511, a young Augustinian monk from Germany came to Rome on church business, and stayed with the friars here. His name was Martin Luther. A few years later, he would start the Protestant Reformation. It is hard to know what he thought of these golden chapels. But it is a strange thought, that he once walked these same floors.

When you step back outside, let your eyes adjust to the light. The obelisk in the centre of the square is ancient Egyptian. It was brought to Rome by the emperor Augustus, and moved here by Pope Sixtus V in the late sixteenth century. Look at the gate to your side, then at the church front, then at the long streets running south into the city. This is how Rome first appeared to so many travellers. Take one more breath of the quiet... and then walk on.