The Tower of Pisa is part of a complex which includes the Pisa Cathedral (Duomo), a baptistery and a cemetery heard. The complex was built as a symbol of power and pride of the wealthy city-state of Pisa. However, especially the tower, a bell tower, is known for centuries because it is tilted.
The tower has eight floors and is 58.4 meters high. The weight of 14,500 tons is on a brick foundation with a diameter of 19.6 meters. The tower is shaped like a hollow tube and is surrounded by colonnades. Inside is a spiral staircase . The tower seems to be built of marble from Carrara, but this is only one covering both the inside and the outside were mounted on a structure of mortar and coarse stones.
Until recently, the foundation tilted south with about 5.5 degrees, making the seventh floor of the tower protruded 4.5 meters compared to the first. After renovations in 2001 and 2008 this was reduced to an overhang 4 meters. Right from the start of construction one has faced the tilt. Eventually showed that the cause of the tilt is twofold, firstly, the soft soil plays a major role the other is the questionable quality of the masonry. Behind the marble cladding and the mortar between the stones were found big holes. By moving the tower, the quality of the masonry has deteriorated further.
The construction of the tower began in 1173 under the leadership of Bonnano Pisano. Soon after the start the construction began swing to the north. On the north side by the vaults above to make the builders tried to straighten out the tower. The construction was halted in 1178 when there were already four floors completed. The construction has finally stopped for almost one hundred years since the residents were involved in a war with Genoa and Florence. Most likely the tower would have collapsed to the soft soil when the construction time was finished. When the construction was resumed in 1272, was the soft clay in the soil, due to the pressure of the already built part, harder. In 1278 the seventh floor was completed, but once more the work was stopped.
Probably the tower collapsed again this time if there would be built by. Between 1360 and 1370, when the clay had become stronger again, the eighth floor, the bell house was completed by Tommaso Pisano. The smooth transition between the seventh and eighth floors can be seen that in 1360 the tower was already quite skewed. The builders have, through additional mortar and masonry, tried to build the last floor perpendicular to the ground.
Several architects have tried for centuries to preserve the tower for a final collapse, which was proved to be not an easy task. When the foundation on the overhanging side would be propped the tower on the other hand was shaken. And when the tower would be pulled up with cables, the masonry would collapse. The numerous studies and efforts to save the tower yielded in additional problems.
Shifted as the tower was in the seventies of the twentieth century, 12 mm by sucking groundwater and the deviation from 1930 in 1990 doubled to 5.5 degrees. In 1999 began the land from the soft top layer slowly removed, leaving the soil slowly subsided. In this way the deviation of the tower was with a half a degree less a method that can be repeated later. The adjustments in 2001 and 2008 have ensured that although the tower is currently skewed but stable condition.
The leaning tower is a popular attraction for many tourists. Since the Middle Ages, the tower was shown on an updated list of the Seven Wonders of the World. In 1987 the tower was added to the World Heritage list of UNESCO.