Their light was a bundle of burning cane that gave them maybe thirty feet of visibility in the best conditions and that had to be managed carefully — a torch dropped in water was gone; a torch blown out by a passage draft had to be relit from the ember before the darkness became complete.

Going 2.5 miles underground with that kind of light, in a passage system where one wrong turn leads to a passage that leads to another passage that leads nowhere and where the sameness of limestone walls makes orientation difficult — this was not casual.

It was the kind of activity that required genuine expertise, genuine knowledge, and genuine courage.

The ancient miners had all three.

They developed the expertise through practice.