Why is Roman concrete so durable? We may have a clue.

http://www.sciencedaily.com/releases/...new discovery about Roman Concrete

Lake Avernus, the Phlegraean Fields, are something you might remember from history books—or Roman studies: the lake no bird could fly over, the Fields of Fire that figure in Virgil’s Aeneid and the contact with the Cumaean Sibyl, or prophet…

Well, the Campi Flegrei are still active, and it is a European supervolcano, a little removed from Vesuvius, itself a very dangerous volcano.