The Hindenburg Line was a series of defensive fortifications adopted by the Germany Army in the third year of World War I.

After a series of devastating battles in 1916, the German Army was no closer to a breakthrough on the Western Front. Having to fight on two fronts, propping up an increasingly tottering Austria-Hungary in the east, Germany was facing the daunting prospect of maintaining a long line of positions that required increasing numbers of manpower and weapons to defend. The German government had floated a peace proposal, which the Allies had rejected. The German high command decided to pull back behind a well constructed line of defense, in order to consolidate the position in the west so the focus could shift to the east, with the hope of ousting Russia for good. During the latter months of 1916 and into the following year, German armies completed the Hindenburg Line.

The Siegfriedstellung, as Germans called it, was a 50-mile-long system of fortified and entrenched positions that stretched from Arras to Soissons. The English name was after Paul von Hindenburg, who made a name for himself defeating Russia in the east and in September 1916 replaced Erich von Falkenhayn as Germany's Chief of the General Staff. After a tour of the front lines, Hindenburg concluded that with no troops to spare, the divisions already fighting against the French and U.K. troops at Verdun and the Somme would get no reinforcements. Following the suggestion of a lieutenant general, Georg Fuchs, Hindenburg ordered a modified retreat, to first construct the Siegriedstellung and then deploy behind it.

The Hindenburg Line was part of an overall defensive strategy in the west. The German high command ordered built four other "Lines" as well:

• The Flanders Position reached from the Belgian coast to Lille
• The Wotan Position went from Lille to Sailly
• The Hunding Position ran from Pêronne to Etain
• The Michel Position stretched from Etain to Pont-à-Mousson.

Some of these Lines weren't finished when troops settled in behind them. When they were all done, they featured two main trenches, about 600 feet apart. (Tens of thousands of workers and prisoners of war dug the trenches.) After that was a rear battlezone, full of downed bridges, flooded lowlands, and mines. Any enemy soldiers making it through such obstacles would also be facing German artillery fire from troops lying in wait, many ensconced in pillar boxes, at the very rear. Buried underground all along the line were telephone cables; railway lines completed a supply line from the heart of Germany.

German forces trooped behind the line under the cover of winter, when neither side had appetite for an offensive. As well, some German forces engaged in a ruse, convincing more than one Allied commander that an attack was imminent. The Alberich Maneuver, as it came to be known, took 35 days to complete. By mid-April 1917, the Hindenburg Line was finished and its defenders behind it.