Based on original documentary sources, A. Hamilton Thompson analyzes the development of the general principles of fortification architecture in Britain in the Middle Ages. Considering the evolution of the art of fortification, the author describes in detail the defensive structures of Britain at different stages of history: early earthen and wooden fortifications, the Norman castle with its main tower - the donjon, which then appeared fortresses with living quarters inside the fortress wall. And finally, it traces the gradual transition from the construction of fortresses to the construction of fortified mansions.