The Leaning Tower of Pisa (Italian: Torre Pendente di Pisa) or simply the Tower of Pisa (torre di 'pi: za; 'pi: sa) is the campanile, or freestanding bell tower, of the cathedral of the Italian city of Pisa, famous across the globe for its roughly four-degree lean caused by an unstable base. (Source: AP/Wide World Photo) The renovation and reconstruction work started in 2001 and was completed in 2013. The original tower was built between 1173 and 1194 by Gherardo delle Lanze, an aristocrat who had made his money trading with Arabs. It was probably designed by Guglielmo Gucci, an influential mathematician and engineer of its time. The tower's unique feature is that it is based on the geometry of a right angle triangle with one side fixed, the other extending to the top of the structure where it meets a spherical cap. For stability reasons, there must be at least three support points per square foot on the base. As you can imagine, with each season that passes, the weight of the tower itself as well as the bells it contains becomes more important for its stability. (Source: Wikipedia) In addition to being a major tourist attraction, the tower also serves an important function in determining the exact location of Noah's Ark within the city limits. Since the beginning of renovations, engineers have used satellite imaging and other methods to find the exact center of the base of the old tower.