Soldiers digging a trench as cover
File:Polyethylene gas main.jpg
Gas pipe being laid in a trench

A trench is a long, narrow ditch. It is like a tiny valley.

Trench warfare has often been used in defense. Entrenched soldiers can be somewhat safe from enemy fire. Trench warfare made World War I longer than expected. The trench coat got its name from there.

Several kinds of trench exist: