The high explosives revolution and its effect on fortification • A walk along the Western Front from Nieuport to Belfort
1914: the Belgian fortresses, the surprising power of super-heavy artillery, and the still more surprising power of improvised field fortification • 1915: the year of deadlock
1916: the year of Verdun and the Somme • 1917: the peak of German defence in depth
1918: the reappearance of semi-mobile warfare
Early warning • Protection • Maximising firepower • Habitability
Siting defences • The organisation of the lines in depth
i) The pre-war permanent fortresses • ii) Hasty or improvised fieldworks
iii) The evolving generations of planned trench lines
Some starting points for fortification tourism on the Western Front