Trenches are battle paths dug into the earth for the purpose of protecting troops from enemy attacks. They were never used as much as during the First World War, but they do not date from that time.
Since the modern period (17th - 18th centuries), trenches have been dug for the siege of strongholds and towns. The poliorcetics is then skilfully organized:the trenches are built in three series of parallels before taking the place.
In the 19th and early 20th centuries, several conflicts were distinguished by the use of trenches:
* The Crimean War especially with the siege of Sevastopol in 1855.
* The Civil War, in the United States, notably the sieges of Vicksburg (in 1863) and Peterburg (June 1864-April 1865)
* The Boer War in South Africa
In 1914, when the French and German adversaries froze in their positions, the use of trenches took on a new dimension with a continuous front that extended over 750 kilometers from the North Sea to the Vosges.
Trenches are meant to protect soldiers from horizontal fire and enemy sight. These are casings dug in the ground, in zig zag or crenellations to avoid firing in a row. There are shelters, lookout and care posts, machine gun nests, they are accessed by trenches also dug into the ground.
The protection they offered has become more relative with the invention and use of balloons and observation planes and shrapnel shells, then chemical weapons produced industrially and used on a large scale in 1914-1918.
On the enemy side, they are made less accessible by networks of barbed wire and other obstacles. It will therefore be the job of the sapper companies to dig galleries to plant explosives directly under the enemy trenches, faster than the enemy does under theirs if possible. This is the origin of the huge craters (or "pots"), some of which can still be seen in the former Red Zone.
For all these reasons, and because of the mud, the rats, the lice, the flies, the proximity of the corpses or the friends or enemies who were dying for days sometimes a few meters from the trenches, life in the trenches of 1914 -1918 was particularly difficult, being partly the cause of many psychological and health consequences for the soldiers of the "great war".
After the war, many adjoining trenches and casemates were poorly filled or poorly cleaned, and sometimes filled with hazardous waste (ammunition, unexploded ammunition), still causing collapses decades later (eg during the construction of the TGV nord ) and remaining sources of environmental risks.