Naples Geology: Tuff and the Underground City

Naples sits on volcanic deposits from ancient eruptions (including the Campanian Ignimbrite). The porous, workable tuff allowed vast underground development.

Geology 101

• Tuff: consolidated volcanic ash, porous, and workable.
• Stability: strong when structured; careful with spans and loads.
• Moisture: microclimates influence conservation and visitor comfort.

Visitor Takeaways

• Tuff is soft to carve, strong when structured.
• Temperature is stable; sound carries.
• Moisture patterns tell seasonal stories.

Curiosity: Look for tool marks and layering in walls — geology written in lines.

Reading Walls

Bottom Line

The stone itself is the technology — enabling aqueducts, defense, and refuge.