IT TOOK TWO CENTURIES TO BUILD IT.
Construction on a campanile, or bell tower to accompany the public cathedral in the Italian riverside city of Pisa broke ground in August 1173. By 1178, workers had made it to the third story of the structure, which was already tilting slightly to the north. Military conflicts with other Italian states would soon halt progress on the tower, which would not resume until 1272. This time, construction only remained underway for 12 years before another war again stopped the work. A final wave of construction picked up again in the early 14th century, concluding with the installation of a bell chamber in 1372.
Source by: http://www.msn.com/en-us/travel/article/13-straight-facts-about-the-leaning-tower-of-pisa/ss-BBrifQM#image=2