Construction on the world-famous Leaning Tower of Pisa, the bell tower of the Pisa Cathedral, began in 1173. However, construction was halted numerous times as the tower began to lean as its weight began to destabilize the ground beneath. It took some 200 years to complete the tower. With a lean that continued to progress even after its completion, the tower underwent thorough repairs from 1990 through 2001, which are intended to keep it from falling over for the next 200 years.