Who Built the Leaning Tower of Pisa? The Architects Behind the Iconic Tilt

The Leaning Tower of Pisa was not the work of one architect but a multi-generational effort spanning 177 years (1173–1350).

Key Figures

• Bonanno Pisano (or possibly Gherardo di Gherardo) – Traditionally credited with the initial design and first phase (1173). Construction halted at the third floor due to sinking.
• Giovanni di Simone – Resumed work in 1272; added four floors, attempting to correct the lean by making one side taller. Halted again by war (1284).
• Tommaso di Andrea Pisano – Completed the bell chamber (7th floor) in 1319.
• Giotto di Bondone – Sometimes associated with later phases; more likely contributed to the adjacent Baptistery.

Why It Leans

The tower sits on soft marine clay and sand over a former estuary. The shallow foundation (3m deep) compressed unevenly. Builders compensated by angling upper floors, giving the tower its banana curve.

Modern Stabilization

1990s–2001 engineering project (soil extraction, counterweights, anchors) reduced tilt by 45 cm and secured it for centuries.

The tower is the campanile (bell tower) of Pisa Cathedral, part of the Piazza dei Miracoli UNESCO site.