Forget Italy's most famous active volcano, Mount Vesuvius, which destroyed Pompeii in 79 AD. The most dangerous volcanic threat in Italy today is one you've probably never heard of: the Campi Flegrei, or Phlegraean Fields. stretching 200 kilometers (125 miles) beneath the bay of Naples and the islands of Capri and Ischia to the outskirts of Naples, is a giant caldera or depression left by a supervolcano some 2 million years ago.It is now home to several volcanoes that have been active for 39,000 years, many of which lie underwater.