Sant'Ivo alla Sapienza

Start in the courtyard. Long arcades of pale stone run down both sides, and your footsteps sound faintly off the old paving. The noise of the street fades behind you. Then you look up at the far end, and you see a small white spiral. It turns around and around above the rooftops, like a shell or a corkscrew pointed at the sky. That spiral belongs to Sant'Ivo alla Sapienza, one of the strangest and most brilliant churches in Rome.

The name says a lot about this place. Sapienza means wisdom, and for centuries this building was home to the University of Rome. The university took its nickname from the palace itself. Today the palace houses the State Archive of Rome, so the corridors around you are full of documents rather than students. The church was built as the university chapel, a place of prayer set at the very centre of a world of books and lectures.

The church is dedicated to Saint Ivo, a medieval priest and lawyer from Brittany, in north-western France. He became the patron saint of lawyers, and he was remembered for defending poor people in court for free. A chapel for a law faculty could hardly have a better patron. So when you stand here, you are standing in a church built for scholars, under the protection of a saint known for justice.

The courtyard came first. Its long arcades were designed in the late sixteenth century, largely by the architect Giacomo della Porta. When the next architect arrived, he inherited a tight space. He had to fit a church into the narrow end of an existing rectangle. Most architects would have accepted a plain, quiet solution. This one did not. His name was Francesco Borromini — and this small church is often called his masterpiece.

Borromini worked on Sant'Ivo through the 1640s and 1650s. His project lasted through the reigns of three different popes. That is not just a historical footnote. Each pope left his family symbol on the building, and you can find them if you know where to look. The church carries the signatures of its patrons the way an old book carries the stamps of its owners.

The first pope was Urban VIII, from the Barberini family. Their symbol was the bee. Look for small bees carved into the stonework. Legend has it that the floor plan of the church itself is shaped like a bee, with its body and wings spread out. Historians are not convinced by this tale. But it is a lovely idea to keep in mind as you look at the walls. The later popes added their own marks: a dove with an olive branch for Innocent X of the Pamphili family, and a heap of small mountains with a star for Alexander VII of the Chigi family.

Now look again at the front of the church. The facade at the end of the courtyard curves inward, as if the building is breathing in. Above it, the drum of the dome pushes outward. Concave below, convex above. Borromini loved this tension. He treated stone as if it were soft clay, bending walls that every rule of the time said should be straight.

If the church is open when you visit, step inside. The first surprise is the colour. Almost everything is white. There are no rich marble panels, no gilded ceilings, no crowded frescoes on every surface. After the gold and colour of so many Roman churches, this whiteness feels almost modern. Your eye is free to follow the shapes alone — and the shapes are extraordinary.

Here is the secret of the plan. Borromini based it on two equilateral triangles laid over each other, forming a six-pointed star. Then he shaped the edges of that star, so that some walls curve in and others are cut flat or rounded out. The result is a space that seems to change as you turn your head. Stand in the centre and slowly rotate. The walls rise without a break into the dome, so you cannot easily say where wall ends and ceiling begins.

Now look straight up. The dome follows the same star-shaped pattern all the way to the top. Lines of decoration run upward and narrow toward a single bright opening. Small winged heads of cherubs and rows of stars climb the curves. Light falls from the lantern above and spreads across the white surfaces. Many visitors feel as if the whole church is drawing them upward, toward that one point of light.

Back outside, the spiral lantern deserves a second look. No one is completely sure what Borromini meant by it. Some scholars connect it to ancient towers or to images of the Tower of Babel. Others see a symbol of wisdom climbing step by step toward truth — a fitting idea for a university. At the very top, a flaming crown and a cross finish the climb. The shape was unusual in Rome, and it still catches people by surprise.

Borromini is often remembered as the great rival of Gian Lorenzo Bernini, the sculptor and architect whose fountains fill nearby Piazza Navona. Bernini was charming and well connected. Borromini was known as difficult and intensely private. His life ended in tragedy. Yet his buildings, small and complex, have inspired architects for centuries. Sant'Ivo is a few minutes' walk from the Pantheon and from Piazza Navona, so you can see the two rivals' work on the same afternoon.

Before you leave, stand once more at the far end of the courtyard. Let your eyes travel from the curved facade, up through the dome, to the turning spiral and the small iron crown at the top. Listen to the courtyard — the quiet steps, the soft voices, the distant traffic beyond the walls. Then, as you walk back out into the street, glance up between the buildings. You may catch one last glimpse of that white spiral above the roofs of Rome.