Leaning tower of Pisa

[riley]

Why does the Leaning Tower of Pisa lean?

[SRAYN1]

Work on building the marble bell-tower start in 1173 and it was leaning within a year. The cause is attributed to unstable soils, possibly a filled-up riverbed or sea formation under its foundation. The original architects, in a vain attempt to correct the inclination, continued to build the tower vertically, so the tower bent in on itself in a banana-shape. By the late 20th Century, the 190ft tower had begun to lean so alarmingly that it was closed to visitors in 1990 for work on the foundations. Engineers shored the tower up with heavy cables and then excavated earth from underneath. It is now 5cm (2in) straighter than it was, but still leans 5.2 metres (17ft).