Leaning Tower of Pisa

Stand still for a moment on the grass and look up. The marble catches the light in pale bands of white and soft grey, and the whole column seems to tip quietly toward you. Around you there is a constant murmur of voices in a dozen languages. Somewhere nearby, someone is holding out both hands, pretending to push the tower back upright. You are in the Piazza del Duomo in Pisa, and the building in front of you is one of the most photographed mistakes in the world.

It is worth remembering what this tower actually is. It is a bell tower, a campanile, built to serve the cathedral beside it. The tower was never meant to be the star of this square. The cathedral was the main event, and the round baptistery across the lawn completed the set. Together these buildings, with the monumental cemetery along the northern wall, form a group that UNESCO listed as a World Heritage Site in 1987.

To understand why Pisa built so grandly, picture the city in the eleventh and twelfth centuries. Pisa was then a maritime republic, a sea power that traded across the Mediterranean. Its ships carried goods between Italy, North Africa, the islands and the eastern ports. That trade brought great wealth home. The cathedral project began in the second half of the eleventh century, and the white marble square became a public statement: this small city was rich, confident, and connected to the wider world.

Work on the bell tower began in 1173. Who designed it is still debated. Tradition has often linked it to the sculptor Bonanno Pisano, and some scholars point to an architect named Diotisalvi, but the records are not clear. What is clear is that the builders ran into trouble very early. Only a few years in, as they reached the third storey, the tower began to sink and tilt. The ground beneath it is soft, a mix of clay, sand and silt left by the rivers.

Then came a long pause. Pisa was at war for much of the following decades, and construction stopped for almost a century. This delay may have saved the tower. During those quiet years, the soil underneath had time to settle and compress. If the builders had kept stacking heavy marble without a break, many engineers believe the whole structure would have collapsed in the Middle Ages. Sometimes a city's troubles turn into a building's good luck.

Here is a detail most visitors miss. When work started again, the builders tried to correct the lean as they went. They made the upper storeys slightly taller on one side than the other. As a result, the tower is not straight at all. Look carefully from the side and you may see a gentle curve, almost like a banana. It is a medieval attempt to bend the tower back toward vertical, one floor at a time.

The tower was finished in stages over roughly two centuries. The bell chamber at the very top came last, in the fourteenth century. Seven bells hang up there, one for each note of the musical scale. Look at the layers below the belfry. There are rows of open arcades, slender columns and rounded arches, wrapped around a hollow cylinder of stone. This style is Pisan Romanesque. Romanesque means the round-arched style of medieval Europe, and here it takes a light, almost lace-like form.

Now for a story you have probably heard. Legend has it that the scientist Galileo Galilei, who was born in Pisa, dropped two balls of different weights from the top. The aim was to prove that they fall at the same speed. It is a lovely image. But historians doubt it ever happened. The tale comes from a biography written by one of his students many years later, and Galileo himself does not seem to describe it. Treat it as a good legend, not a documented event.

Over the centuries the lean slowly grew worse. Some attempts to help actually made things worse. In the 1930s, workers injected grout into the foundations, and the tower tilted further. By the late twentieth century, experts were seriously worried. In 1990 the tower was closed to the public. An international team of engineers and scientists began a long rescue. For more than a decade, nobody climbed these stairs.

The solution was patient and surprisingly gentle. First, engineers placed hundreds of tonnes of lead weights on the north side, the side opposite the lean. Later they used drills to remove small amounts of soil from beneath that north side. Slowly, the ground settled there, and the tower eased back. By the time it reopened in 2001, the lean had been reduced by around forty centimetres. Later monitoring found the tower had stopped sinking further.

That is the second surprise. Engineers did not want to make the tower straight. A straight tower in Pisa would be a strange loss. The goal was only to make it safe for a few more centuries. Today it still leans by roughly four degrees, and it is a little under sixty metres tall. Look across the lawn, too. The baptistery and the cathedral also sit on this soft ground, and they carry slight tilts of their own.

If you climb, the experience is very physical. There are around three hundred worn marble steps, spiralling up inside the walls. The steps are hollowed in the middle from centuries of feet. As you rise, you feel the lean in your body. On one side you seem to walk uphill, on the other side downhill. At the top, the red roofs of Pisa spread out around you, with the river Arno and the hills beyond.

Before you leave, step back toward the edge of the lawn. Notice how the tower, the cathedral and the baptistery line up in the afternoon light, all built from the same pale stone. Listen to the voices, the laughter, the click of phones. People have stood here for more than eight hundred years, staring at this tower. It was a problem from almost the first day. And yet it has stayed up. As you walk away, look back once more. It is still leaning, still standing.