At the crossroads of via del Quirinale and via delle Quattro Fontane, where the traffic never stops and four seventeenth-century fountains sit against the corners of the buildings, there is a facade that moves. It swells and recedes like stretched fabric, and above the door it carries a date carved in stone: MDCLXVII, 1667.
This is the church of San Carlo alle Quattro Fontane, which everyone in Rome calls San Carlino. It is the first building Francesco Borromini put up on his own, and it was also the last site still active when he died.
A hundred metres further along the same street stands Bernini’s Sant’Andrea al Quirinale. The two churches look at each other from close range, and side by side they tell the story of Roman Baroque better than any textbook.
This one, though, takes twenty minutes to visit and costs nothing.
How small it really is
The church measures roughly twenty metres long by twelve wide. Those are the dimensions of a large flat, not of a Roman church.
That is where the affectionate diminutive everyone uses comes from, and where the comparison the sources have always repeated comes from too: its footprint would fit inside one of the four piers holding up the dome of St Peter’s. It is a figure of speech rather than a surveyed measurement, but it says more than any number: what in the Vatican is a piece of wall is here an entire sacred building with its own dome.
Why would an architect of nearly thirty-five take on a commission this small? The patrons were the Spanish Discalced Trinitarians, an order with no money. Borromini offered to work for them without a fee, because after years spent drawing for other men this was his chance to sign something with his own name.
The result is that the materials are poor by choice as much as by necessity: brick, travertine, stucco. Not one coloured marble, not one gilding to pull the eye. In a city that was filling up with polychrome marble at exactly that moment, it was almost a statement.
The site that runs across his whole life
The commission arrives in 1634. The convent buildings and the cloister come before the church, because the friars had to live there in the meantime; the church is built between 1638 and 1641 and consecrated in 1646.
Then something happens that is worth keeping in mind while you look at the facade: for more than twenty years that facade is not there. Borromini only starts it in 1664, at the end of his life, and in 1667 he dies before it is finished.
It was completed from his drawings by his nephew Bernardo Borromini, who worked on it through the following decade; the statue of St Charles Borromeo went into the central niche around 1680.
So the date carved under the cornice, that 1667 you can read from the street, is both the year the lower order was completed and the year of his death.
Why it feels taller inside than it is
You step in, and the first impression is of a space larger than the outside promised. How does a church twelve metres wide avoid feeling cramped?
The interior is entirely white: no colour breaks the surfaces up, so the eye reads the space as a single block. The plan is neither a circle nor a cross but an oval obtained by bending the walls, and the walls do not stand still: they recede and push forward, with columns that accompany them instead of dividing them.
Then there is the dome, and it is the reason to go in. It is oval, and its coffers are not all the same: crosses, hexagons and octagons interlock and shrink as they rise towards the lantern. That is the trick that stretches the dome upwards.
The light comes from the lantern and from windows you cannot see, hidden behind the rim of the oval: the dome seems to light itself.
Look at it for a full minute with your head tipped back. It is the thing visitors miss most often, because they walk in, go round the room in thirty seconds and walk out.
The cloister, where you understand the method
From the church you pass into the cloister, and this is where Borromini’s working method reads without any need for explanation.
The courtyard is tiny. A normal cloister would have four right angles, and in a space this narrow those corners would have felt like a cage. Borromini cuts them off: at the corners the columns shift diagonally and the perimeter becomes an elongated octagon, so the eye runs on instead of hitting a wall.
The columns are plain, the parapet on the upper floor alternates upright and inverted balusters, and there is a well in the middle. There is not a single precious material in the whole courtyard.
The crypt and the tomb he never used
Under the church there is the crypt, which repeats the plan above with low vaults and walls hollowed out by niches. It is as white as the church and almost always empty, and on a weekday afternoon you can have it to yourself.
On one side a small octagonal chapel opens up. Borromini had designed it for his own burial.
He never ended up there. On the evening of 1 August 1667, after months of decline, he wounded himself with his own sword, and he died on the morning of 2 August, after dictating his last wishes. He asked to be buried in another church, San Giovanni dei Fiorentini, in the same tomb as Carlo Maderno: the relative who had brought him to Rome as a boy and taught him the trade.
Above his first work, then, an empty room is still waiting for him.
Practical information
Details checked on 30 August 2026 on the church’s own site, run by the Trinitarians.
Tickets. Admission is free. Inside there is a box for donations towards maintenance, which here is not a detail: the community is small and the building is fragile.
Opening hours. Weekdays from 10:00 to 13:00 and from 15:00 to 17:00 between October and April, from 16:00 to 19:00 between May and September. At weekends the church is closed to visitors; Sunday mass is at 11:00. Groups wanting to come outside those hours have to ask in advance through the website.
What you can see. Church, sacristy, cloister and crypt. Capacity is about forty-five people, so in high season you may wait a few minutes outside.
Audio guide. You listen on your own phone, with nothing to hire.
Getting there. Via del Quirinale 23. The handiest metro stop is Barberini (line A), from which you walk up via delle Quattro Fontane in five minutes. From Repubblica it is the same distance on the other side.
How long. Twenty minutes for church, cloister and crypt without rushing. An hour if you add Sant’Andrea al Quirinale, which is on the same street.
When to go. Early afternoon, when the light comes through the lantern and the dome separates from everything else.
Two hundred metres downhill, on the same via delle Quattro Fontane, stands Palazzo Barberini: the site where Borromini had worked as an assistant and left his spiral staircase, today the National Gallery of Ancient Art, with Raphael’s Fornarina and two Caravaggios. The ticket can be booked online.
What to see nearby
A hundred metres away, on the same street, is Bernini’s Sant’Andrea al Quirinale: same period, same road, opposite budget and opposite result. It is the comparison that tells you the story of Bernini and Borromini better than any anecdote.
Walking down towards Piazza Barberini you find Palazzo Barberini and its artworks, the Triton Fountain and the Bee Fountain, all within three hundred metres of each other.
On the other side of the centre, in Piazza Navona, are the Fountain of the Four Rivers and the facade of Sant’Agnese in Agone, where Bernini and Borromini once again ended up working a few metres apart.
Photo credits. Facade: Alexkom000, CC BY 4.0. Dome: Fiat 500e, CC BY-SA 4.0. Cloister and crypt: Livioandronico2013, CC BY-SA 4.0. All from Wikimedia Commons.
