Tower of Pisa

Construction on the Tower of Pisa began in 1173 and took nearly 200 years to build due to war and other disruptions. Due to the soft ground and poor foundation, it almost immediately began to lean. By 1990, the tilt had reached 5.5 degrees. The structure was stabilized by remedial work between 1993 and 2001, which reduced the tilt to 3.97 degrees. The height of the tower is 55.86 metres (183 feet 3 inches) from the ground on the low side and 56.67 m (185 ft 11 in) on the high side. The width of the walls at the base is 2.44 m (8 ft 0 in). Its weight is estimated at 14,500 tonnes (16,000 short tons). The tower has 296 or 294 steps; the seventh floor has two fewer steps on the north-facing staircase. Galileo Galilei, who lived in Pisa at the time, is said to have dropped two cannonballs of different masses from the tower to demonstrate that their speed of descent was independent of their mass, in keeping with the scientific law of free fall.