"Tuff" is a soft yellow volcanic rock that is an outstanding building material, in great abundance underneath Naples.
So Neapolitans in quarrying
rock below ground to be used above ground as the building material for
temples, bathhouses and mansions, creating a vast system of tunnels, passageways,
grottos, cavities, caverns, caves, catacombs, and cemeteries.
Expeditions in Naples
SUBTERRANEAN
NAPLES
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World Travel Magazine
By
Heike Schmidt
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to one million people, Naples is built on an ancient system of tunnels
and passageways...