Throughout France is a vast network of canals and navigable rivers that lead through a wondrous variety of pastoral settings, medieval towns and villages and vibrant cities. Along the way are vestiges of human habitation spanning the millennia from palaeolithic times onward through a complex history of settlement. The occupation and taming of the land followed the courses of the rivers and crossed the low passes that link them to each other. The canals were built to aid commerce here in the seventeenth, eighteenth and nineteenth centuries and much of the original engineering is still in...