across Mont Cenis
This was the easiest route into Italy, across southeastern France from Chambery to Turin in northwestern Italy. The Mont Cenis Pass rises to only 6825 feet. This was Napoleon's invasion route to Italy in 1796, and thereafter the post-road was improved to allow uninterrupted traffic between the two countries. It was this road, indeed, that the Shelleys themselves would take shiortly after publication of the novel, in March 1818, on their trip to Italy.