The ancient mount Vesuvius rises high above the Campanian plain. The plain – a great oval ringed by mountains – stretches north, east and south for hundreds of kilometres. Along its northern edge, the river Volturno, the longest river in Italy, flows to the sea.  Below Vesuvius is a great bay: the Bay of Naples, although it will be well more than a thousand years before new arrivals from the Greek island of Euboea build a city here which will bear that name. We are Italy’s deep past, although the very idea of Italy is yet to be invented. Vesuvius is not the only volcano here. It is part of…