Trench warfare is the type of land warfare using occupied lines largely comprising military trenches, in which troops are well-protected from the enemy's small arms fire and are substantially sheltered from artillery. It became archetypically associated with World War I (1914–1918), when the Race to the Sea rapidly expanded trench use on the Western Front starting in September 1914.
Trench warfare proliferated when a revolution in firepower was not matched by similar advances in mobility, resulting in a grueling form of warfare in which the defender held the advantage. On the Western Front in 1914–1918, both sides constructed elaborate trench, underground, and dugout systems opposing each other along a front, protected from assault by barbed wire. The area between opposing trench lines (known as "no man's land") was fully exposed to artillery fire from both sides. Attacks, even if successful, often sustained severe casualties.
The development of armoured warfare and combined arms tactics permitted static lines to be bypassed and defeated, leading to the decline of trench warfare after the war. Following World War I, "trench warfare" became a byword for stalemate, attrition, sieges, and futility in conflict.
Field works have existed for as long as there have been armies. Roman legions, when in the presence of an enemy, entrenched camps nightly when on the move. The Roman general Belisarius had his soldiers dig a trench as part of the Battle of Dara in 530 CE.
Trench warfare was also documented during the defence of Medina in a siege known as the Battle of the Trench (627 AD). The architect of the plan was Salman the Persian who suggested digging a trench to defend Medina.
There are examples of trench digging as a defensive measure during the Middle Ages in Europe, such as during the Piedmontese Civil War, where it was documented that on the morning of May 12, 1640, the French soldiers, having already captured the left bank of the Po river and gaining control of the bridge connecting the two banks of the river, and wanting to advance to the Capuchin Monastery of the Monte, deciding that their position wasn't secure enough for their liking, then choose to advance on a double attack on the trenches, but were twice repelled.