Saint Isaac's Cathedral

Stand still for a moment and look up. A dome of gold sits high above the rooftops of Saint Petersburg, and on a bright day it throws light back at the sky. Under your feet the ground feels solid. But this city was built on marsh, and the building in front of you had to fight that soft, wet earth before a single column could rise.

This is Saint Isaac's Cathedral. For many years it was the largest church in Russia, and its dome is still one of the first shapes you notice from almost anywhere in the city centre. From the river, from rooftops, from the far end of a long avenue, that gold dome is there. Up close, though, the scale changes. You stop seeing a landmark, and you start seeing stone, bronze and an enormous amount of human labour.

Why Saint Isaac? He is not a well-known saint in the West. Isaac of Dalmatia was an early Christian monk from Byzantium, the eastern Roman Empire. His feast day falls on the same day as the birthday of Peter the Great, the tsar who founded this city in the early eighteenth century. So this church honours a saint, but it also honours the city's founder. Several earlier churches dedicated to Saint Isaac stood in this area before the present building. This one is the grandest, and the last.

The architect was a Frenchman, Auguste de Montferrand. He was young and not yet famous when Tsar Alexander the First approved his design. Construction began in 1818 and the cathedral was consecrated in 1858. That is about forty years of work. Montferrand spent most of his working life on this single building. He saw it finished, and he died only weeks later.

Now think about the ground again. To keep the cathedral from sinking into the marsh, builders drove thousands of wooden piles deep into the soil. On top of them they laid a heavy foundation of stone. Most visitors never think about this part, because it is completely invisible. Yet everything you see — the columns, the walls, the dome — rests on that hidden forest of timber below the square.

Look at the porticoes, the great columned porches on each side. The red granite columns are monoliths. Each one is cut from a single piece of stone, and each weighs more than one hundred tonnes. The granite came from quarries on the coast of what is now Finland. Workers moved the columns by water, then raised them into place with wooden scaffolding, ropes and teams of men turning large winches. Contemporary drawings show crowds gathering to watch the lifting, as if it were a public performance.

Here is a detail many people walk past. On the western side, look closely at the columns and the walls near their base. You can see chips and scars in the granite. These are marks from artillery shells during the Second World War, when Leningrad — the Soviet name for this city — was under siege for almost nine hundred days. The marks were left in place on purpose. They are a quiet record of those years, cut into the stone.

The siege touched the cathedral in another way too. The gold dome was easy for enemy gunners to see, so it was painted a dull grey to hide it. Inside, the cellars became a store for treasures taken from palaces and museums around the city, to protect them from bombing. A building made to praise God and the empire became a shelter for the city's art.

That gold on the dome has a darker story. It was applied with a method called fire gilding. Gold was mixed with mercury, spread over the copper, and then heated until the mercury burned off. The fumes were poisonous. Accounts from the period say that many workers became ill or died from this work. Exact numbers vary between sources, so take any single figure with care. But the danger was real, and it was well known at the time.

There is also a famous piece of folklore about the scaffolding. Legend has it that a prophecy said the Romanov family, the ruling dynasty, would last only as long as scaffolding stood around Saint Isaac's. Because of constant repairs, scaffolding appeared on the building again and again for years. It is a good story. But treat it as a city legend, not as recorded history.

Inside, the cathedral feels very different from the grey square outside. The walls and columns are covered with coloured stone, marble and mosaics. Near the altar, look for the tall columns of green malachite and the smaller ones of deep blue lapis lazuli. These stones were rare and very expensive. Many of the large religious pictures here are not paintings at all. They are mosaics, made from thousands of tiny pieces of coloured glass, so they would not fade or decay in the damp northern air. Above the altar is a large stained-glass window showing Christ. Stained glass like this is unusual in Orthodox churches, and it is one more sign of the mix of Western and Russian taste in this building.

The twentieth century changed the cathedral's purpose. After the revolution, the Soviet state closed it as a church and turned it into a museum, for a time with an anti-religious message. In 1931 a Foucault pendulum was hung from the dome. A Foucault pendulum is a long, slow-swinging weight that shows the rotation of the Earth. It was a scientific statement in a religious space. Today the building works mainly as a museum, though church services are held here again on some occasions.

If you have the energy, there is a walkway around the colonnade high up on the drum of the dome. The climb is long and narrow, but the reward is a wide view over the rooftops, the river Neva, and the golden spire of the Admiralty nearby. From there you can see how the city was planned: long, straight streets, wide water, and low skylines broken only by domes and spires.

Before you go, step back to the edge of the square and look once more. Notice how the bronze angels stand along the top of the drum, holding their lamps. Notice the colour of the granite in the changing light, and the small dark scars near its base. Somewhere beneath your feet are those old wooden piles, still holding everything up. As you walk away, turn around now and then. The dome will follow you down the street for a long time.