St John's Co-Cathedral

Outside, the stone is plain. Warm, honey-coloured limestone, the same stone you see on almost every building in Valletta. The facade is flat and almost severe, framed by two bell towers. Nothing about it prepares you for what waits behind the doors. Step inside, let your eyes adjust... and the whole space turns to gold.

This is St John's Co-Cathedral, the church of the Knights of Saint John. They were a military and religious order that ruled Malta for more than two centuries. After they defeated the Ottoman siege in 1565, the Knights built a new fortified capital on this peninsula. That city was Valletta. And at its heart, they needed a church of their own.

The building went up in the 1570s. Its designer was Girolamo Cassar, a Maltese military engineer who also worked on many of the city's early buildings. That background shows in the exterior. It looks more like a fortress than a palace of faith. The walls are thick, the lines are sober, and the decoration is kept to a minimum. Cassar built for a city that still expected another attack.

The change came in the seventeenth century. The Knights hired the Italian painter Mattia Preti, who spent years transforming the interior. He carved the stone walls into rich Baroque patterns. Baroque, here, means a dramatic style full of movement, gilding and theatrical light. Then Preti painted the long barrel vault above you. Look up. The ceiling tells the life of Saint John the Baptist, the patron saint of the Order, in a series of scenes.

Here is the first detail many visitors miss. Preti did not paint those scenes on canvas and fix them to the ceiling. He painted directly onto the stone. He prepared the surface with oil, and he worked high on scaffolding for years. Some of the figures at the edges seem to sit on the architecture itself, as if they are leaning over the cornice to watch you.

Now look down. The entire floor of the nave is a carpet of marble tombstones. There are around four hundred of them. Each slab marks the grave of a knight or an important official of the Order. The stones are inlaid with coloured marble — reds, greens, yellows, black and white. You will see coats of arms, crowns, angels, and Latin inscriptions praising the dead.

And you will see skeletons. Some hold hourglasses. Some carry scythes. Some seem to grin. These images remind the living that time is short. For men who spent their lives at war on the sea, that message was close to home. It is strange to stand on a floor so full of death and find it so colourful, almost joyful. That is part of the Baroque way of thinking.

Along both sides of the nave, you can see a row of side chapels. The Knights came from across Europe, and they were organised into groups by language and region. Each group was called a langue. Each langue had its own chapel here, and each one competed to decorate it more richly than its neighbours. Walk slowly past them. Notice how the style and the saints change from one chapel to the next.

You may wonder about the word co-cathedral. Malta already had a cathedral, in the old inland city of Mdina. That remained the seat of the bishop. In the early nineteenth century, the Pope allowed this church to share cathedral status with Mdina. So the island has two cathedrals, and this one is the co-cathedral.

The church has not always kept its treasures. In 1798, Napoleon's army took Malta from the Knights. French troops removed silver and other valuables from the building, and much of that metal was melted down. Some of the empty spaces you notice today are the result. The gold you see now is mostly gilding on carved stone — and the soldiers could not carry that away.

Now, follow the signs to the Oratory. This room was built for prayer and for the training of young knights. It holds the most famous painting on the island: The Beheading of Saint John the Baptist, by Caravaggio. He painted it in 1608, during his short stay in Malta. It is enormous. Most of the canvas is dark, with a few figures caught in hard light.

Here is the second surprise. This is the only painting that Caravaggio is known to have signed. Look closely at the red pool of blood flowing from the saint's neck. The signature is written inside the blood. It is a quiet, unsettling detail. Caravaggio was a brilliant painter with a violent life, and he had fled to Malta after killing a man in Rome. Not long after this work was finished, he was in trouble again here and left the island.

In the same room, look for a second Caravaggio. It shows Saint Jerome writing at a table, an old man bent over his book beside a skull. It is smaller and calmer than the beheading. Comparing the two is worthwhile. One is loud and public. The other is private and still. Together they show how wide this painter's range could be.

Before you leave, walk back into the main church and stand near the centre of the nave. Let the noise of the other visitors soften. Look from the stone floor, to the gilded walls, to the painted vault, and back again. When you step outside, the plain limestone facade will look different. You know now what the Knights kept behind it. Notice the bright light of the square, the cafés nearby, the stone under your feet. The whole city is built of that same pale stone.