The team of engineers from has worked for more than 20 years to ensure that the tower doesn't fall over. It is now one-and-one-half inches straighter than it had been.

It was not the first such effort. In 2001, engineers finished off another slant-reducing effort, removing 17 inches by removing soil from the foundations and installing large amounts of braces and lead counterweights. That recalibration took more than a decade. An earlier effort, in the 1920s, involving injecting cement grouting into the tower; that, too, worked, for a certain extent.

As of this latest stabilization work, the tower is 186 feet high on its tall side and 183 feet high on its shorter side.

Construction on the marble bell tower began in 1173 but didn't finish for another 200 years. The tower started to lean almost from the beginning, but the builders didn't correct the lean. The ground underneath is particularly soft because it used to be a river. And yet, the tower has withstood several strong earthquakes through the years. Scientists have found that the surrounding itself has embraced the Tower so thoroughly that the requisite ground motion of a strong earthquake doesn't affect the Tower.