Trenches were built during World War I to protect stalemated troops on both sides from artillery and rifle fire. Although the war began with rapid movement of the German army, when the Allied forces stopped the Germans, both sides dug trenches to help avoid losing territory they had gained.
By late 1914 when the Germans and Allies confronted each other, technology, such as heavy artillery and machine guns, precluded the efficiency of a frontal attack. Hundreds of miles of trenches were dug on both sides with empty areas between known as no man's land. The length of the trenches made flanking maneuvers impossible.
Elaborate networks of barbed wire were strung up to prevent enemy soldiers from advancing. Little forward progress was made by either side in four years, but the trenches did not prevent the troops from incurring heavy casualties. Artillery bombardments frequently decimated frontline trenches. Often, officers ordered frontal attacks that brought about heavy casualties on both sides.
Because trench warfare during World War I was so prolonged, it evolved patterns of construction and operation. The parapets, or fronts, of the trenches were about 10 feet high and usually reinforced with sandbags. Because snipers were a constant threat, periscopes and mirrors were used to observe the battlefield. Trenches were designed in zigzag patterns so enemies that penetrated defenses were limited in their lines of fire. Several parallel lines of trenches were dug, and soldiers rotated between the front trenches, support trenches and reserve trenches.