leaning Tower of Pisa

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The Leaning Tower of Pisa (July 2006)
The Leaning Tower, diagonally behind the east-facing cathedral (2014)

The Leaning Tower of Pisa ( Italian Torre pendente di Pisa ) is probably the most famous inclined building in the world and the symbol of the city of Pisa in Italy .

The tower was planned as a free-standing bell tower ( campanile ) for the cathedral in Pisa . 12 years after the foundation stone was laid on August 9, 1173, in 1185, when the building had reached the third floor, the tower stump began to slope towards the southeast. The building was then dormant for around 100 years. The next four floors were then built with a smaller angle of inclination than the existing one in order to compensate for the inclination. After that, construction had to be interrupted again until the bell chamber was also completed in 1372 .

The reason for its inclination lies in the subsoil made of loamy mud and sand, which deforms under the weight. According to the latest excavations, the tower stands on the edge of a former island right next to an ancient harbor basin that was already silted up at the time of construction. At the end of the renovation work, the tower is tilted around four degrees, corresponding to a deflection at the top of 3.9 m (at a height of around 55.8 m). Inside the tower hangs a pendulum , which is fastened in the upper middle and almost touches the side wall due to the tilt at the bottom.

According to legend, Galileo Galilei , who came from Pisa, discovered the laws of fall while trying to fall from the tower .

In 1987 the ensemble of the tower, the cathedral , the baptistery and the cemetery was declared a World Heritage Site by UNESCO .


The Leaning Tower, behind the cathedral, view from the west - Tele / Detail (2013)
Cathedral and Leaning Tower of baptistry seen from
Schematic drawing with dimensions
Close up of the entrance area

The 55 meter high and 12 meter diameter campanile consists of 14,200 tons of white Carrara marble and has seven bells, which were not allowed to ring for a long time because of the risk of collapse. It should be the highlight of the whole complex of the Piazza dei Miracoli . It differs from the usual square towers of central Italy and is in great contrast to the pointed towers of northern Europe. It rests on a spiral foundation made of 700 m³ rubble and mortar. The month and year of the start of construction are chiseled next to the entrance: August 1173. In documents, however, 1174 is always mentioned, because according to the calendar of that time, the new year began on March 25th for the Pisans. Giorgio Vasari called Bonanno Pisano and a certain Guglielmo the original architects of the tower.

The campanile had another function besides that it was supposed to carry the bells. In the event of external danger, the clergy fled into the tower. Wall openings and projections in the cylinder shaft made it possible to insert beams and floors in every floor if necessary.

Each floor has a door to the column gallery, which consists of 30 columns each. On the south side, six steps lead up to the bell house, on the north side only four. The stairs to the top viewing terrace are said to have inspired Brunelleschi to build a similar staircase to the lantern on the dome of the cathedral in Florence .

From January 7, 1990, the 14,500-ton tower had to be closed to visitors because the incline became too dangerous. There was a worldwide call for structural engineers to work out and submit the best solutions for stabilization.

After 13 years of renovation work, during which the tower was raised again by 44 centimeters, it has been open to tourists again since December 2001. Visitors can climb the tower every quarter of an hour (as of 2016) in groups of a maximum of 40 visitors for a period of 15 minutes.

The Leaning Tower of Pisa is not the most crooked building or the most crooked tower in the world, as is often assumed. Nevertheless, it is one of the most crooked structures that - planned upright - unintentionally got into a tilted position.


Surname Casting year Caster diameter Mass (approx.) Chime Arched opening
Assunta 1654 Ioan Petrus de Orlandis 1,596 mm 2,600 kg h 0 Northeast, below
Crocifisso 1818 Santio Gualandio da Prato 1,436 mm 1,800 kg cis 1 Southeast, below
San Ranieri 1735 Pier Francesco Berti 1,247 mm 1,150 kg dis 1 South, below
Pasquereccia 1262 Locterineus de Pisis 1,040 mm 1,014 kg g sharp 1 Southwest, below
Del Pozzo 2004 (refill) Fonderia Marinelli di Agnone 942 mm 490 kg g 1 West, below
Terza 1473 Antonio di Jacopo 817 mm 330 kg h 1 Southwest, above
Vespruccio 1501 anonymous 572 mm 120 kg e 2 South, above

As a static precaution, the seven church bells of the cathedral are only struck by means of internal electromagnetic hammers, at noon at noon and before masses.

Before that, the bells were used liturgically according to their names, for example the terza for the third, the third hour of the liturgical day, i.e. at 9 a.m., or the Vespruccio for Vespers, 6 p.m. The ringing was done by hand; on feast days the bells were  swung full - a slancio -.

The smallest bell from 1501, called Vespruccio , has a very slim, sugar-hat-like shape. The Del Pozzo bell is a true-to-original cast of its predecessor, cast by Nicolaus Castellum in 1606.

Remedial measures

Attempts in the Middle Ages to save the building through special construction measures such as sloping floors and thinner and lighter walls on the overhanging side did not have sufficient effect, so that only 54 meters of the originally planned 100 meters height were built.

Since accurate measurements began in 1911, the slope has increased steadily, and the rate of increase doubled from the 1930s to 1990. That year the annual increase in slope was 6 arc seconds. In addition, the survey showed that it was a rotational movement, with the center of the circle at the level of the floor of the first gallery perpendicular to the center of the tower at floor level, which itself did not perform any vertical movement. During two heavy rainstorms in 1995 an increase in inclination in the order of magnitude of an arc second could be determined within a few hours. From this it was concluded that the cause was not - as is commonly assumed - the creeping of the soft marine clay layer (horizon B from a depth of about 10 m to a depth of 40 m, where horizon C begins with dense marine sand), but rather the overlying horizon A (sand, sandy and clayey silts), in which storms with heavy rainfall that occur regularly in September to December triggered increased rotation.

Lead ingots as a counterweight (summer 1998)

Various renovation measures had been undertaken since the temporary closure in 1990. In May 1992 the campanile was secured with steel tires on the second floor, as dangerous cracks had appeared in the supporting marble. A total of 18 of these tires were installed. In addition, in July 1993, 600 tons of lead ingots were stored in the foundation as a counterweight on the north side. As a result, the inclination of the tower could be reduced by one minute of arc in 1993. In 1995 further renovation measures (ground freezing and steel cable anchoring) were carried out because the lead weights were perceived as disturbing. As a result, however, the inclination increased. As a result, the higher side of the foundation at its ledge on the outside of the tower was weighted down again in September 1995, this time with 900 tons of lead ingot (see picture), which stopped the incline.

A committee of international experts, which should decide on the renovation measures of the tower (1990 to 2001 under the direction of Michele Jamiolkowski ), could not commit itself to any specific measures and was therefore dissolved by the Italian government at the end of 1996. However, after the great earthquake in September 1997, the committee was reinstated. In autumn 1998 a majority agreed on a new measure to rehabilitate the campanile, the so-called soil extraction method (planned by John Burland based on an idea by the engineer Fernando Terracina from 1962). For this purpose, inclined holes were drilled in the ground (depth around 4 to 5 m, within horizon A) under the northern part of the tower, so that around 50 m³ of material was removed. The earth slowly sagged, and eventually the bottom of the tower too, and the whole tower rose increasingly to the north. The total incline of the tower was reduced from 5.5 degrees before the start of the renovation work (around 1990) to around four degrees. The tower is thus likely to be secured for the next 300 years. After the completion of the renovation measures, the tower was opened for inspection again on December 15, 2001.

To secure it during this work, the tower was secured in 1998 with two strong steel cables 103 meters in length so that it could not collapse due to unexpected movements.

During construction work to secure the building, an old Roman road was discovered, which was still recorded in old plans, as well as a medieval grave with a complete skeleton.


  • John B. Burland, Michele B. Jamiolkowski, Carlo Viggiani: The stabilization of the Leaning Tower of Pisa .. In: Soils and Foundations. Volume 43, number 5, 2003, pp. 63-80, doi : 10.3208 / sandf.43.5_63 .
  • John B. Burland, Michele B. Jamiolkowski, Carlo Viggiani: Leaning Tower of Pisa: Behavior after Stabilization Operations. In: International Journal of Geoengineering Case Histories. Volume 1, Number 3, 2009, pp. 156-169, ( online (PDF; 3.04 MB) ).
  • John B. Burland: The Enigma of the Leaning Tower of Pisa. 6th Buchanan Lecture, 1998, ( online (PDF; 1.53 MB) ).

See also

Web links

Commons : Leaning Tower of Pisa  - Collection of images, videos and audio files

Individual evidence

  1. Andreas English: The secret of the sailors of Pisa. In: Hamburger Abendblatt from June 16, 2004
  2. World record in East Friesland - the most crooked tower in the world. In: sueddeutsche.de . May 17, 2010, accessed December 4, 2015 .
  3. Initially, a half-hour visitor cycle was set up. The tickets can also be booked online in advance.
  4. Pretty weird: the Guinness Book selects the most crooked building in the world. In: Spiegel Online . June 9, 2010, accessed December 4, 2015 .
  5. ^ Film recording of the ringing of the bell from 1933
  6. Kölner Stadt-Anzeiger , May 19, 1992.
  7. ^ Burland, Jamiolkowski, Viggiani: The leaning tower of Pisa. Behavior after stabilization operations. Leaning Tower of Pisa: Behavior after Stabilization Operations. In: International Journal of Geoengineering Case Histories. Volume 1, Number 3, 2009, pp. 156-169.
  8. ^ Don Barker: Stabilizing the Leaning Tower. In: Architecture Week , July 11, 2001.
  9. Kölner Stadt-Anzeiger , April 14, 1997, p. 36.
  10. ^ John B. Burland: The Enigma of the Leaning Tower of Pisa. 6th Buchanan Lecture, 1998.
  11. ^ Fernando Terracina: Foundations of the tower of Pisa. In: Géotechnique. Volume 12, number 4, 1962, ISSN  0016-8505 , pp. 336-339, doi : 10.1680 / geot.1962.12.4.336 .
  12. ^ Microsoft Encarta

Coordinates: 43 ° 43 ′ 22.8 "  N , 10 ° 23 ′ 46.7"  E