The Leaning Tower of Pisa is one of the architectural wonders of the world, and permanently fascinating to people.
The famous bell tower has stood for over six centuries.
But it hasn't ever stood straight—at one point in history, the tower tilted about 4.5 meters from the vertical!
Pisa is an ancient city in Tuscany, Italy.
Located on the river Arno, with easy access to the sea, the city became a major port of trade.
In the eleventh century, merchants from across the Mediterranean and as far away as the Middle East came to buy and sell goods.
The city's inhabitants, the Pisans, often had to defend their city against outside forces.
They also made their own conquests. In 1063 they sailed to the island of Sicily and attacked the city of Palermo.
The defeat of Palermo made the Pisans rich and confident in their power.
They decided to build a large cathedral to show off their treasures.
A large piece of open land sat in the middle of the city, which the Pisans called the Square of Miracles.
They decided to build the cathedral on the square, as a tribute to Pisa's conquests and rich heritage.
The front of the building was covered with stones stolen from ancient Roman ruins.
Even today you can read ancient Roman inscriptions, some of which are upside down or sideways, in the marble stones of the cathedral.
The building took a very long time to complete, almost three hundred years.
The Pisans also decided to build a cemetery and a tall bell tower in the square.
Construction of the bell tower, which would later become known as the Leaning Tower of Pisa, began in 1173.
Not long after the workers had laid the foundation and built the first three floors, they noticed that the building was sinking on the south side.
This was not surprising because the soil underneath the Square of Miracles was very marshy.
It was a common problem for buildings in the area.
In fact, the name Pisa means "marshy land" in Greek.
Around this time war broke out, and construction on the bell tower stopped for nearly one hundred years.
This long interruption turned out to be good for the tilting tower.
It gave the building's foundation time to settle, and probably even prevented it from collapsing long ago.
Experts believe that when construction on the tower restarted, an engineer named Bonanno Pisano was in charge of the challenging project.
In order to compensate for the building's tilt, Pisano decided to make the columns and arches on the south side a little longer.
He believed that this would level out the tower.
But Pisano's solution only worsened the problem.
The extra weight made the tower sink some more!
As years passed, other engineers and builders took on the challenge of finishing the building, and fixing its tilt.
By 1350 the tower's bell chamber had been constructed, and the rest of the tower was finally completed around 1372.
When the tower was finished, many people were glad that all the builders had not quit the project.
It was truly an architectural wonder, with beautiful arches and two hundred marble columns.
But by now the tower's tilt was very noticeable.
The tilt fascinated people, yet it worried them too; one day the tower could collapse.
Over time many efforts were made to save the tower.
Some of the solutions were realistic, while others were almost comical.
One person suggested draining all of the water beneath the foundation of the tower; another suggested leaving the water there but freezing it!
Other ideas included moving the tower to another location or rebuilding it.
In the 1920s experts tried injecting cement into the foundation of the tower in order to stabilize it, or at least slow the rate at which it was tilting.
Despite all these engineering efforts, the tower continued sinking.
By the 1960s the Italian government was so concerned about the tower,
they announced that they were looking for suggestions to solve this puzzling problem.
Finally, in 1990, it was decided to close the building for safety reasons.
A major project was eventually launched to straighten the tower.
This time engineers slowly removed earth from underneath the foundation on its north side.
When the tower reopened in 2001, the tilt had been reduced by about 44 centimeters!
And over time the tilt decreased even more.
The tall tower, with its unusual tilt, has fascinated not just builders and tourists.
Galileo Galilei, a former resident of Pisa, was born about two hundred years after the tower was finished.
He used it to conduct many important scientific experiments.
In one famous story, Galileo wanted to prove his theory that all objects fall at the same speed.
So he climbed to the top of the Tower of Pisa and dropped two balls at the same time.
According to the story, both balls hit the ground at the same time even though they differed in weight.
Today the bell tower continues to draw tourists and admirers from around the world.
Engineers believe, due to recent measurements, that the building will remain stable now for at least two hundred years.
So for generations to come, people can continue to look in amazement at the Leaning Tower of Pisa.