The reason why the Leaning Tower of Pisa is tilted can be attributed to both design and geological factors.
Construction of the tower started in 1173 and the lean was already evident during its construction due to the soft ground on which it was built. The tower was constructed on a ground composed mainly of clay, silt, and fine sand, causing the foundation to sink on one side, leading to its characteristic tilt.
In addition to the soft ground, design flaws, and inadequate foundation also contributed to the tilt. The tower was built with a shallow foundation and the weight of the structure was not distributed evenly, causing the tilt to worsen over time.
Several attempts have been made to stabilize and straighten the tower, including the removal of soil from the higher side and adding counterweights, which have successfully reduced the tilt to some extent. However, the tower will always retain its famous lean due to its historical and cultural importance.