Vesuvius is a “Somma-stratovolcano,” meaning its current cone is located inside the caldera of an older, larger volcano (Mount Somma). It is the only volcano on the European mainland to have erupted within the last hundred years (last eruption in 1944). Because over 3 million people live in its immediate vicinity, it is considered the most densely populated volcanic region in the world. Modern monitoring systems are in place to provide early warnings, but its history of explosive Plinian eruptions makes it a constant concern for Italian authorities.