From Haaretz.com: Archaeologists Uncover Vast Ancient Roman Mining Operation in Spain.
Archaeologists excavating the ancient city of Munigua in southern Spain have found a vast Roman copper mining operation built on an older mine dating back thousands of years.
Exploitation of ore at Munigua apparently began by the Turdetani, the original inhabitants of the region, over 4,000 years ago. Now the excavators have discovered an elaborate system of ventilated underground galleries connected by tunnels dating to the Roman era.
They also found shafts connecting at various heights forming floors that let the miners extract metal deeper than had been believed possible at the time. Happily for the miners, the ancient Romans were on to the secret of ventilation. [continue]