The Western Front's trench lines grew out of a failed race to outflank
In autumn 1914, German and Allied armies each tried to slip around the other's open end, digging in every time they were blocked. Within weeks the leapfrogging had carried two matched lines of trenches from the Swiss border to the Belgian coast. Those lines barely shifted until the German offensive of March 1918.
Digging in was ancient. Thucydides described trenches in the Peloponnesian War, and at the siege of Alesia Julius Caesar surrounded his works with a 20-foot trench plus two inner ditches, each 15 feet wide and deep, which he flooded. In the seventeenth century the Ottomans developed systems of parallel trenches linked by zigzag approaches that let besiegers creep toward a fortress under cover, and the French engineer Vauban turned the idea into a standard method of three parallels.
The American Civil War offered a preview. Around Petersburg, Union lines were layered into rear areas, a main battle line and a forward zone with firing holes, with log-covered bomb-proof shelters against shelling. What they lacked was barbed wire; defenders relied instead on the open ground an attacker had to cross.
By 1914 firepower had leapt ahead of mobility. Rifles, machine guns, and rapid-firing field guns such as the French 75 could cut down troops crossing open fields long before they arrived. The French trusted in headlong attack, the Germans invested heavily in howitzers and machine guns, and the British had no formal doctrine at all. Nobody had planned for defence in depth. Early trenches were shallow ditches meant to be packed shoulder to shoulder, which proved disastrous under artillery, so fronts came to be held more thinly while trench systems deepened into interlocking networks of four or five lines. A proper trench needed to be at least 2.5 metres deep so men could walk upright unseen. British guidance reckoned that 450 men working six hours at night could dig 250 metres of front-line system; digging from the surface was fastest, but only safe in darkness or out of sight.
Supply was the other brake. Artillery consumed ammunition on an unprecedented scale, and horse-drawn carts could not haul it far beyond the railheads, so even successful attacks stalled. Only motor transport in the next war broke that limit. The human cost left traces in art as well as history: in 1916 Auguste Rodin produced a drypoint for the donation receipts of an American hospital in Paris that treated injuries to the face and jaw.
Source: Trench warfare
