Barbed Wire
Barbed wire was a very good defense. Barbed wire would halt soldiers on foot due to the razors and metal points that would slice, poke, and ensnare troops. Barbed wire was put around trenches to keep enemy soldiers out and spread across battle feilds to keep advances slow. Tanks could easily run over barbed wire and make a safer path for troops, but the flattened barbed wire could still be a tripping hazard.
The barbed wire was also used for traps. The barbed wire would ensnare soldiers by tearing into their skin and clothes, keeping them trapped, until they died. These traps would usually be rows of fences made of barbed wire that soldiers would be forced to crawl under in order to advance causing them to be trapped under.