Landmark Europe
Leaning Tower of Pisa
The Leaning Tower of Pisa is a tall, round bell tower in Italy. It tips to one side! Engineers helped it stay up safely.
The Leaning Tower is the bell tower of Pisa's cathedral, in Italy. Building began in 1173, and the tower started to lean while workers were still on its second floor, because soft ground lay under shallow foundations. It is 58.36 meters tall, has seven bells and 273 steps, and engineers made it safe between 1990 and 2001.
Begun in 1173 and finished in 1372, the campanile of Pisa Cathedral tilted early in its construction as its shallow foundation settled into soft subsoil. Its builders bent the upper floors to compensate. An international committee led in the engineering by John Burland reduced the lean by about half a degree with soil extraction, and the tower reopened in 2001.
Photo: Chabe01, CC BY-SA 4.0, via Wikimedia Commons
Discover the Leaning Tower
The Leaning Tower is in Pisa, a city in Italy.
It is round and white, with rows and rows of little arches. It does not stand up straight. It tips to one side! Bells ring at the very top.
The Leaning Tower stands in Pisa, a city in the Tuscany region of Italy, on a wide green lawn called the Piazza del Duomo, the Cathedral Square. It is not a castle tower and was never used to defend the city. It is the bell tower of the cathedral next to it.
The tower is round, made of stone and pale marble, and 58.36 meters tall. It tilts by about 5 degrees, which is easy to see from the lawn. People notice the lean first, but the Opera della Primaziale Pisana, which looks after the square, also praises the beauty of its architecture.
The tower is the campanile, or freestanding bell tower, of Pisa Cathedral. With the cathedral, the baptistery and the Camposanto cemetery, it forms the Piazza del Duomo, a group UNESCO inscribed as a World Heritage Site in 1987. UNESCO says the four medieval buildings were erected between the 11th and 14th centuries and greatly influenced monumental art in Italy.
The Opera della Primaziale Pisana, the body that looks after the square's monuments, gives the tower's figures: 58.36 m tall, 15 m in external diameter, 14,453 tonnes, and a current inclination of about 5.115 degrees. It stresses that the tower never served to defend the city: its job was to mark time for the cathedral with its bells.
- Height
- 58.36 m
- Lean today
- about 5.115 degrees
- Building began
- 1173
- World Heritage Site
- Piazza del Duomo, Pisa (1987)
A bell tower for a rich port city
Long ago, Pisa was a busy city of ships and sailors.
Pisa built a big new church. Then it began a tall bell tower beside it. The builders worked very slowly. It took them about two hundred years!
In the Middle Ages, Pisa was a maritime republic, a city-state whose ships sailed across the Mediterranean Sea. In 1064 it began a new cathedral, and in 1173 work started on its bell tower.
About five years later, when the builders reached the second floor, the tower began to lean. Work often stopped, sometimes for decades at a time, and the tower took nearly 200 years to finish. It was completed in 1372. Its largest bell was cast later, in 1655.
UNESCO dates Pisa's greatest prosperity from the 11th century to 1284; the new cathedral was founded in 1064, and a 12th-century relief by the sculptor Biduino at the tower's entrance shows two ships and a lighthouse, celebrating Pisa as a maritime republic. Work on the tower started in 1173. In the 16th century Giorgio Vasari wrote that "it is said" a Guglielmo and the sculptor Bonanno laid its foundations in 1174 and, knowing little about building on Pisa's ground, saw it tilt before they were halfway up; the Opera quotes this as Vasari's account, not as proven fact.
According to Imperial College London, the lean began after construction reached the second floor in 1178. The Institution of Civil Engineers (ICE) says work was slow and sometimes abandoned for decades, as Pisa was often at war with other city-states such as Florence and Genoa, and that the tower was completed in 1372, nearly 200 years after it was begun.
Why it leans, and how builders coped
The tower stands on soft, squishy ground.
Its base under the ground is not very deep. So the tower sank a bit on one side and began to tip. The builders kept going. They made the top floors a little bit bent.
The tower's foundations go only about 3 meters into the ground, and the soil beneath them is soft and unstable. As the heavy stone tower rose, one side sank more than the other, and it began to lean.
The builders did not give up. On the upper floors, they made one side a little taller than the other to make up for the tilt. That is why the tower is slightly curved as well as leaning. It was built from 29,424 cut stones, and its columns have 207 carved tops called capitals.
ICE attributes the lean to shallow foundations of 3 m on unstable subsoil. Later builders tried to correct for it by building the upper floors with one side shorter than the other, so the structure is curved as well as tilted; ICE notes that some later interventions made the problem worse, and by the 1990s there were fears of collapse.
The Opera's figures describe the scale of the masonry: 29,424 hewn stones covering 7,735 square meters, 207 capitals and a staircase of 273 steps, for a total weight of 14,453 tonnes. Individual craftsmen can be named: the Opera credits Biduino and his workshop with the 12th-century "Capital with Monkeys" on a half column of the ground level and the relief of ships at the entrance. No opened source gives a number of workers.
Arches, steps and seven bells
The tower has many floors of little arches and columns.
Inside, a long staircase goes round and round to the top. At the top hang seven bells. Each bell has its own musical note.
The tower is wrapped in rows of arches held up by slender columns, floor after floor. At the bottom, the ground floor has tall arches built into the wall. Inside, a staircase of 273 steps winds up to the top.
At the very top hang seven bells, one for each note of the musical scale. The biggest was made in 1655 and weighs about three and a half tonnes. For safety, children may climb only if they turn 8 by the end of the year (2026 rules).
The cylinder is 15 m across and wrapped in open galleries of arches on columns, above a ground level of blind arcades on half columns. A staircase of 273 steps climbs inside, and the Opera counts 207 capitals in all.
The bell chamber holds seven bells, one for each note of the musical scale; the Opera says they marked time for the cathedral. The largest, cast in 1655, weighs 3.5 tonnes. The Opera calls the tilt a "miracle of statics": a tower of more than 14,000 tonnes leaning about 5.1 degrees. Climbing is by timed ticket, and for safety children who will not turn 8 by the end of the year are not allowed in (2026 rules).
- Steps
- 273
- Bells
- 7
- Largest bell
- about 3.5 tonnes, cast in 1655
- Outside width
- 15 m
Saving the tower
The tower kept tipping a tiny bit more each year.
So engineers made a plan. They took a little soil from under the high side. The tower leaned back a little. Now it is safe to visit again.
Year after year the tower leaned a little more, and by the 1990s experts feared it could fall. In 1990 it was closed to visitors, and the Italian government asked a team of experts, led by the British engineer John Burland, to save it.
They did not try to make it straight. Instead, they gently drilled out small amounts of soil from under the north side, the side opposite the lean, so the tower settled back by about half a degree. They also put in drains to control the water underground. The tower reopened in 2001, and a 2013 study found it stable.
The tower closed to the public in 1990, when the Italian government appointed an expert committee; the engineering was led by John Burland, professor of soil mechanics at Imperial College London. (ICE says 13 experts, Imperial says 14 members.) The chosen method, soil extraction, used inclined holes just beneath the north side of the foundation (the tower leans south) to remove small amounts of soil in a controlled way. Imperial says 38 cubic meters were removed, straightening the tower by 45 cm to where it stood in 1838; ICE gives 38 cm and a reduction of about half a degree.
The team also found that the tower tilted more in winter, when rain raised the water table, and installed drains under the north side. Imperial reports that engineers announced in May 2008 that the movement had been stopped, and that restored stonework was revealed in April 2011. A 2013 study found the tower "stable but tending to straighten," 2.5 cm more since 2001.
Amazing facts
-
The tower has seven bells, one for each musical note.
The tower's seven bells each ring a different note of the musical scale.
Seven bells, one for each note of the scale, hang in the bell chamber; the largest, cast in 1655, weighs 3.5 tonnes.
-
The tower is a little bit curved, not just tipped.
Builders made the upper floors a little taller on one side to make up for the lean, so the tower is curved as well as tilted.
Upper floors were built with one side shorter than the other to compensate for the tilt, so the shaft is curved as well as inclined.
-
A stone carving of monkeys sits on the tower.
One of the carved column tops at the bottom of the tower is called the "Capital with Monkeys."
The 12th-century "Capital with Monkeys" on a ground-level half column is credited to the sculptor Biduino and his workshop.
-
Engineers made the tower lean a tiny bit less.
Engineers did not make the tower straight. They reduced its lean by about half a degree, just enough to keep it safe.
Soil extraction reduced the inclination by about half a degree, while keeping the famous tilt.
Words to know
- bell tower
- a tower that holds bells, often built beside a church; also called a campanile
- foundation
- the solid base under a building that holds it up
- tilt
- to lean or slope to one side
- capital
- the carved top of a column
- soil
- the loose earth that covers the ground
- engineer
- a person who uses science and math to design and fix structures and machines
Discovery challenge
-
What kind of tower is the Leaning Tower?
What was the Leaning Tower built to be?
What role does the tower play in the Piazza del Duomo?
- A bell tower
- A lighthouse
- A castle tower
Show the answer
A bell tower
A bell tower! Bells ring at the top.
It is the bell tower of Pisa's cathedral. It was never used to defend the city.
It is the cathedral's campanile, marking time with seven bells; the Opera stresses it never had a defensive role.
-
Why does the tower lean?
Why did the tower start to lean?
What caused the tower's tilt, according to ICE?
- Soft ground under a shallow base
- It was built leaning on purpose
- Strong winds pushed it
Show the answer
Soft ground under a shallow base
The ground is soft, so one side sank a little.
Its foundations are only about 3 meters deep, on soft soil, so one side sank more than the other.
Shallow foundations of 3 m on unstable subsoil; the tilt appeared once building reached the second floor.
-
How many bells are at the top?
How many bells hang in the tower?
How many bells does the bell chamber hold?
- Three
- Seven
- Twelve
Show the answer
Seven
Seven bells, one for each musical note.
Seven bells hang at the top, one for each note of the musical scale.
Seven, one per note of the scale; the largest, cast in 1655, weighs 3.5 tonnes.
-
What did engineers take from under the tower?
What did engineers remove from under one side to help the tower lean less?
What did the stabilization team extract from beneath the north side of the foundation?
- Soil
- Bells
- Columns
Show the answer
Soil
Soil! A little soil came out, and the tower leaned back a bit.
They drilled out small amounts of soil under the north side, and the tower settled back about half a degree.
Soil extraction through inclined holes reduced the inclination by about half a degree; drains then controlled the water table.
-
How many steps go up the tower?
How many steps does the staircase have?
How many steps does the Opera count on the tower's staircase?
- 73
- 273
- 1,273
Show the answer
273
273 steps! That is a lot of climbing.
The staircase has 273 steps, winding up inside the tower.
The Opera gives 273 steps, in a tower 58.36 m high.
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Experiments to try
- Watch Try it What If? Lab What if buildings had different foundations? A building's whole weight presses down through its foundation onto the ground. A wide foundation spreads that weight out, like snowshoes on snow. In our model, a 200-tonne building on sand is safe on a 40-square-meter footing. Shrink the footing to 8 square meters and it presses five times harder, more than the sand can take, so the building would sink and could crack or tilt.
- Watch Try it What If? Lab What if a ball were thrown sideways off a tower? Drop one ball from a 20-meter tower and throw another straight out sideways at the same moment. The thrown ball travels about 10 meters away, yet in our model both land at the same moment, about 2 seconds later: moving sideways does not change how fast a ball falls.
- Watch Try it What If? Lab What if a house were built on soft clay? A building presses down on the ground under its foundation. Sand, gravel and rock can each safely carry a different amount. In this lab, a 300-tonne building stands safely on sand. Move it onto soft clay without changing anything else, and see what happens and how to fix it.
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- Watch Try it What If? Lab What if a house were built on soft clay? A building presses down on the ground under its foundation. Sand, gravel and rock can each safely carry a different amount. In this lab, a 300-tonne building stands safely on sand. Move it onto soft clay without changing anything else, and see what happens and how to fix it.
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For parents & teachers
What children will learn
- Locate Pisa in Italy and explain that the tower is the cathedral's bell tower.
- Explain how shallow foundations on soft soil made the tower lean.
- Describe how engineers reduced the lean by removing soil and controlling groundwater.
- Recognize that builders and engineers solve problems over long periods of time.
Recommended ages: 3 to 17 · About 15 minutes
Talk about it
- Engineers chose not to make the tower straight. Why do you think they kept some of the lean?
- The first builders kept going after the tower began to tip. What would you have done?
- Why might the ground under a building matter as much as the building itself?
Try at home or in class
- Stack wooden blocks into a tower on a folded towel and on a hard table. Press gently on the towel side and watch which tower starts to lean.
- Build a block tower that leans a little, then add blocks to the top that lean the other way. Does the tower balance better or worse?
Key vocabulary: bell tower, foundation, tilt, capital, soil, engineer
Where these facts come from
- Wikidata , Wikimedia Foundation (CC0 1.0)
- Tower , Opera della Primaziale Pisana (official site)
- Curiosities , Opera della Primaziale Pisana (official site)
- FAQ , Opera della Primaziale Pisana (official site)
- Piazza del Duomo, Pisa , UNESCO World Heritage Centre
- Why is the Tower of Pisa leaning? , Institution of Civil Engineers
- Prof. who helped save Leaning Tower of Pisa returns to Italy to celebrate 20-year milestone , Imperial College London
- UNESCO World Heritage List , UNESCO World Heritage Centre (Linked as a reference; site facts come from Wikidata)
- Wikimedia Commons , Wikimedia Foundation (Per file (public domain, CC0, CC BY or CC BY-SA); see each media record)
Checked, not yet human-reviewed. Last updated October 24, 2026. Spotted a mistake? Tell us.