All the extinct as well as active volcanoes are west of the Apennines, except Mount Vultur in Apulia. It is these numerous volcanoes which have driven the sea far from the foot of the Apennines, and have enlarged this coast, whereas the opposite shore, where not a single volcano is to be seen, is so narrow ; whence come also those lakes in the midst of ancient craters, and perhaps a part of the marshes. It is known that in 1538 the Lucrine lake was changed into a marsh by a volcanic eruption. The lowest part of the Pontine Marshes is on a line joining Stromboli to the ancient craters of Bolsena and Vico. .