This book is a Tour de Force. I've known about it for a few months now, but didn't expect to ever see it, because of the price. Fortunately someone, knowing my desire to read all things on the Camino, arranged to have it appear as a Christmas gift.
This is a gorgeous book, sized for coffee table display, and full of color photos. Most coffee table books are full of pictures with a few lines of descriptive text. The text in The Roads to Santiago could stand on its own as a work on pilgrimage architecture and history. It clearly was an immense amount of work to write. I wish the authors or publishers had seen fit to mention how long it to complete.
The definitive work still in print on the Camino de Santiago is Gitlitz and Davidson The Pilgrimage Road to Santiago: The Complete Cultural Handbook. That work covers the architecture and history within the borders of Spain. Imagine Gitlitz and Davidson, in color, with bigger and better photos, including the four pilgrim routes through France, and you have some idea of The Roads to Santiago.
This four pound book is something I recommend to someone who has walked the Camino de Santiago, and is thirsty for more information. A few hours with this book and you will be thinking about booking a trip to France and starting down one of the French chemins.