The Leaning Tower was supposed to stand straight and plumb, an imperious monument to the trading power of 12th century Pisa. Built on soft clay, however, the tower began to list only a few years after construction began. Upon completion in 1350, the tower leaned about four and half feet, but as time passed, the angle of the 16,000-ton tower became more precarious. By 1990, the tower leaned about 13 feet off kilter, and nearly two million pounds of lead ingots had to be placed on one of its sides to prevent its collapse. But the nearest the tower has been to destruction had nothing to do with its famed tilt. Allied forces ordered an American sergeant to blow it up during World War II when they thought the Germans were using it as an observation post. Only the reticence of the 23-year-old American saved the tower.