The Leaning Tower of Pisa, whose shoddy foundations have granted it immortal fame, has not only stopped tilting further; it is gradually untilting itself. An international committee established to monitor the listing landmark’s stability has found that 21 years after being pulled back from the brink, the tower is leaning even less. It has lost 4 cm (1.57 inches) of its tilt and moves less than expected.
Nunziante Squeglia, a professor of geotechnics at the University of Pisa who cooperates with the monitoring group, said that the tilt has decreased thanks to stabilization work, along with “oscillations now varying at the average of 1/2 millimeter a year, although what counts the most is the stability of the bell tower, which is better than expected”.
Construction of the bell tower of the Duomo of Pisa began in 1173 in an area where the soft, soggy subsoil spelled disaster from the very first. Crews had only reached the third story when the lean became pronounced. Work was interrupted by war in 1178 and when it resumed in 1272, the soil had stabilized somewhat. Engineers added four more floors and the belfry, adjusting the proportions to compensate for the lean by building one side of the floors taller than the other side.
The lean and subsidence continued undeterred by all attempts to correct them for eight centuries. The tower’s lean increased steadily by an estimated millimeter a year, which adds up when you’re measuring the years by the hundreds. On January 7th 1990, spurred by the tragic and deadly collapse of the 10th century Civic Tower in Pavia the year before, the Leaning Tower of Pisa was closed to the public. At this point it was leaning at a 5.5 degree angle and it was deemed at imminent risk of collapse. Anyone living in apartment buildings potentially in the path of a fall was evacuated and the tower was wrapped in a steel girdle, cabled and anchored to the ground. While it was being kept stable by wires and lead counterweights, massive quantities of soil were being removed from under the high side of the tower.
After 10 years work and 70 metric tons of soil removed, the tower’s lean was reduced to 3.99% degrees and it was 19 inches straighter, a position it had last seen in 1838. In 2001, the newly stabilized, slightly-less-leaning but much-less-fatal Tower of Pisa reopened to the public. It has been monitored regularly since then and is clearly passing with flying colors.