Mt Vesuvius is the world's most dangerous volcano, and it threatens three million people. It was responsible for the most famous natural disaster of ancient history, the eruption that destroyed the Roman city of Pompeii. And its most recent blast was caught on film in 1944. Today Vesuvius is the most densely populated volcano in the world. Now recent scientific discoveries show that it is capable of an eruption larger than ever before thought possible and that hidden beneath Vesuvius there is a vast magma chamber of boiling hot rock, ready to come out.