Deep within Rome’s Celian Hill is a remarkable survivor - an ancient tuff quarry, whose output helped construct many of Rome’s monuments. Tuff is a light volcanic stone, lagrely used as an internal building stone, behind grander facing stones. The quarry is named after the immense 1st century Temple of Claudius (itself now largely destroyed) beneath whose foundations it lies.
It is postulated that the underground space was first excavated for use as a water cistern and many earlier well shafts penetrate the quarry roof, some still used by the convent above. It is just possible it was used as the reservoir which stored water used to flood the Colliseum, during ancient spectacles.
Galleries reach out some distance from the secure entrance; part of the quarry is now flooded with dark and still water. There is some evidence - such as electrical fittings - of reuse during World War II as an air-raid shelter although it is surprising that no apparent affort was made at that time to level out the undulating floors.