Why the Leaning Tower of Pisa Leans (It's Not in Venice!)

First, a correction: the famous leaning tower is in Pisa, Italy—not Venice. It's the campanile (bell tower) of Pisa Cathedral.

Causes of the Lean

1. Weak Foundation Soil: The tower sits on 10 meters of soft marine clay, sand, and shells over denser clay. The north side compresses more.
2. Shallow Foundation: Only 3 meters deep—insufficient for the 14,500-tonne structure on compressible soil.
3. Construction Pauses (1173–1372): Built in three stages over 199 years. Long pauses allowed partial settling, but the lean increased when work resumed.
4. Asymmetric Weight: The south side has more columns/counterweight attempts, but the north side settled faster.
5. High Water Table: Fluctuating groundwater softens clay unevenly.

Stabilization (1990–2001)

Engineers removed 70 tonnes of soil from the north side, installed lead counterweights, and anchored the base with cables. The lean reduced by 45 cm (17 in), returning to 1800s angle. It's now stable for ~200 years. Open to visitors (limited tickets).