The Leaning Tower of Pisa began construction in 1173 but experienced problems when the third floor was built on weak, unstable soil, causing the tower to lean. Construction halted for over a century as the soil settled. When work resumed in 1272, the architect built taller floors on the opposite side to compensate, resulting in the tower's curve. Modern anchoring with steel cables and weights has stabilized the tower, though it remains tilted at 5.5 degrees.