This is an excellent overview of the development of castle architecture and fortifications technology from the dark ages through the wide adoption of gunpowder. The historical narrative is that of English politics, and all the castles described are located within England and Wales, but the general story will be of interest to any medievalist. Sancha's peculiar (in the sense that I've never seen anyone else do it) device is placing drawings atop photographs of existing buildings. Her reconstructions of now-ruined architecture and introductions of people into the pictures effectively draw her readers into the world she wishes to portray.