The Leaning Tower of Pisa

The Leaning Tower of Pisa didn't begin its existence at an angle, but it has remained that way for hundreds of years.

The third-oldest structure in the Italian city of Pisa, the eight-story white marble Tower measures 13.42 feet wide at the base and 8.14 feet at the top. Famously, the Tower leans at an angle of just less than 4 degrees. One side is 186 feet tall; the other side is 183 feet tall.

Construction on the ground floor of the freestanding bell tower began on August 14, 1173. Five years later, with building progressing to the second floor, the ground under the Tower began to sink in unstable soil. Building mostly stopped for 99 years as skirmishes took place between Pisa and Florence, Genoa, and Lucca. (One exception was the installation of clocks on the third floor, in 1198.) In the meantime, the soil beneath the Tower settled a bit but not enough to remove the tilt.

Construction resumed full-time in 1272 and went on for another eight years, during which builders tried to compensate for the tilt by making one side of the upper floors taller than the other. The unintended result is that the Tower is on a bit of a curve as you look upward.