The Economics of Engineering Failure: How a six-foot foundation in unstable soil created a 900-year-old monument that generates €30 million annually, proving that some disasters pay dividends.
The conventional wisdom holds that engineering failures are purely technical problems—structural weaknesses, material failures, or design flaws that must be corrected. Yet economic and tourism data from one of history’s most famous leaning structures reveal a counterintuitive reality: some foundation failures can become extraordinarily profitable assets.
Construction on Pisa’s bell tower began in 1173 with ambitious plans for a 185-foot monument to ecclesiastical power. The structure immediately began sinking into the soft clay and sand beneath it. By the time construction halted in 1372, the tower leaned 5.5 degrees from vertical. The evidence suggests this was no mere oversight, but a fundamental misunderstanding of geotechnical engineering that turned a cathedral bell tower into a global icon.
The initial consensus viewed medieval construction as fundamentally sound, with Gothic cathedrals across Europe standing for centuries. Foundation depths of 20-30 feet (6-9 meters) were standard for major structures, providing stability through sheer mass and depth. The Pisa project followed similar patterns in other Italian cities, where soil conditions were comparable.
However, a deeper analysis of the geological data reveals a more complex picture. The tower sits on alluvial deposits from the Arno River, consisting of alternating layers of clay, sand, and silt with bearing capacities as low as 2-3 tons per square foot (19-29 kPa). The foundation was only 6 feet (1.8 meters) deep and 65 feet (20 meters) in diameter, far below the minimum required for the 14,500-ton structure. The data indicate that settlement began within months of construction, with the tower sinking 2-3 inches (5-7.6 cm) annually.
The Leaning Tower teaches us that foundation failures can have unexpected consequences—sometimes even beneficial ones. But this is the rare exception where failure becomes feature.
When greed drives the design process instead of incompetence, the outcomes are far more tragic and immediate. The Tower took decades to reveal its flaw. Our next disaster killed 20,000 people in minutes.
In our next post, we’ll travel to ancient Rome in 27 AD, where a former slave’s hunger for profit created one of history’s deadliest stadium disasters—and forced the birth of the world’s first building regulations. Continue to The Fidenae Stadium Collapse →
External Sources
- Petroski, Henry. To Engineer Is Human: The Role of Failure in Successful Design. St. Martin’s Press, 1985.
- Petroski, H. Design Paradigms: Case Histories of Error and Judgment in Engineering. (Cambridge University Press, 1994).
- Perrow, C. Normal Accidents: Living with High Risk Technologies - Updated Edition. (Princeton University Press, 2000). doi:10.1515/9781400828494.