Construction was halted for over a century. Workers tried to strengthen the foundation of the building by putting more cement into it. When construction was resumed construction workers tried to compensate the slant by building the uppers storey taller on the side that was sinking in.
The 185-meter-tall Leaning Tower of Pisa is made out of white marble. It weighs about 14000 tons. Inside there are spiral staircases that lead to the bell chamber. A total of seven bells, one for each note of the musical scale, were completed up to the beginning of the 16th century.
In the 1990s authorities closed the tower to visitors. It had reached an angle of 5 degrees. Engineers and restoration workers made efforts to stabilize the tower, which was sinking at 1.2 mm a year. In May 2001, the Leaning Tower of Pisa was reopened to the public. Since then the tower has been under constant observation. In 2008 tourism authorities announced that sinking had stopped and the tower was expected to be stable for the coming centuries. In 1989, the Leaning Tower of Pisa became a World Heritage Site.