• How the Leaning Tower of Pisa tilts but never falls


    The Leaning Tower of Pisa, one of the most popular destinations for Europe travel, is famous mainly for the architectural accident that gave it its nickname, but the full story of how the tower got its lean - and what's being done to keep it upright - is less well known.

    The long fall
    Following work started on the tower in 1173, the structure began to tilt. According to How Stuff Works, the soft soil under the tower's base was not solid enough to hold its weight, causing the building's northward lean. Noticing that the tower was unstable, workers made the columns on one side of the tower's third floor taller to compensate. Just five years after construction began, civil unrest put the project on hold.

    Almost 100 years passed before builders returned to the site in 1272 to find the tower now leaning in the opposite direction due to the shifting soil. Only six years went by before construction was again halted. In 1360, the final leg of building started, lasting until 1370.

    Necessary delays
    Several centuries of delay ended up being just what the tower needed. Discover Magazine reported that, had construction continued on schedule, the uneven ground would have toppled the tower, possibly before it was even finished.

    "In both cases the masons stopped just in the nick of time," soil mechanics specialist at Imperial College London, John Burland, told the magazine. "Because they left it, the weight of the tower squeezed a lot of the water out of the clay, and the clay became stronger."

    ​Lessening the lean
    Burland, along with his friend Michele Jamiolkowski, a geotechnical engineer at the Polytechnic University of Turin, was appointed in 1990 to find a way to reverse the tower's iconic slouch. The year before, a bell tower from around the same period as the Tower of Pisa had collapsed elsewhere in Italy, killing four people.

    To keep the Leaning Tower of Pisa from sharing its fate, the government established the International Committee for the Safeguard of the Leaning Tower to restore it. By the time the committee started its work, the tower was already leaning 5.5 degrees to the south, so far that their computer models would not even accept that the structure could still be standing.

    The entire piazza holding the tower was closed for 11 years while work was done on the tower. After three attempts to save the structure with anchors, weights and braces that were deemed too ugly, the committee found the solution. By digging soil out in small amounts at a time, the ground under the tower would be able to settle safely. Two years of work finally solved the problem. The Leaning Tower remained 13 feet off center, enough to make it safe for visitors for centuries to come while still living up to its name.

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