Following the early battles of 1914 along the Marne and in the Ypres salient, World War I rapidly changed from a war of movement into one of attrition, with the opposing sides entrenching themselves in a line of fortified positions from the Flanders coastline to the Swiss border. This volume details the different styles of fortification used on the Western Front throughout the course of the war, from the early ditches of 1914 to the complicated systems of 1918. It explains the development of the 'defence in depth' German system and the British reaction to it, as well as illustrating the importance of the pre-war forts, particularly around Verdun.