Italy’s famous leaning tower of Pisa is not leaning so much anymore. The tower has self-corrected 4 centimeters, or 1.575 inches, over the last 20 years. Amid fears the ancient bell tower would fall flat in the mid-1990s, an international team of experts installed a system consisting of 750 metric tons of lead weights that not only helped save it from collapsing onto the grass below, but also immediately corrected 2 inches of its famous lean, which made it stable enough to allow visitors inside by 2008 after it had been closed for centuries. The weights apparently have continued to stabilize the structure. The tower started leaning almost immediately after construction began in 1173, when the soft ground below the structure started to settle. The architects in charge of the project started correcting the lean by building the columns slightly taller on the north section about a third of the way up the 186-foot tower, which created a slight curve. The same trick was used on the eighth floor. Prior to the intervention, the tower moved at a rate of about 1.2 millimeters, or .05 inches, each year.
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