Trench warfare is a type of land warfare using occupied fighting lines consisting largely of trenches, in which troops are significantly protected from the opponent's small arms fire and artillery bombardment. Trenches are usually dug in a zigzag pattern, to prevent enfilade fire along the trench-lines. Troops occupying trenches can survive artillery bombardments that would be deadly in the open; although the shells may kill or bury the occupants or collapse the trench itself, such bombardments often fail to destroy an extensive trench network.
While not the first conflict to feature extensive trench warfare, World War I is best known for having large-scale trench systems on both the Western and Eastern Fronts. Other wars featuring significant trench warfare include the Crimean War, American Civil War, the Russo-Japanese War, the Italian Front in World War I, and the Iran–Iraq War.