The Origin Development of the Christian Church in Gaul: During the First Six Centuries of the Christian Era; Being the Birkbeck Lectures for 1907 and 1908 in Trinity College, Cambridge. E-book. Formato PDF T. Scott Holmes   -  Forgotten Books, 2017  - 

A traveller, therefore, entering Gaul from the south, was compelled, by several mountainous regions and a high tableland, to keep to one or other of these two routes we have mentioned. The wide and more open districts of the north could only be reached by these two valleys, and the geographical divisions which these rivers and mountains created could not be ignored.