On The Wire (Barbed Wire That Is.)
Wire with barbs that cause people or animals discomfort when trying to get through it. An easy concept with a number of variations that has a number of uses. Originally designed as a cheap and effective way to contain cattle on the plains, it was not long before it was re-purposed for the military.
Most of the wars fought in the late 19th century and up to WWI. saw barbed wire in use in various forms. It was cheap. It was quickly deployed. While not so much a fortification it was very effective against infantry and cavalry. So it worked.
During WWI it was used extensively. It could either survive or at least be quickly repaired in the wake of the massive artillery bombardments of the day. Unfortunately, the birth of armored warfare sort of ended the heyday of barbed wire on the battlefield. Tanks were much more effective at getting through it than man or beast.
Above is a version of barbed wire called concertina wire. It has a similar design but is stored and deployed in large coils. These rolls can be set up in a number of different configurations. Weel beyond what regular bared wire could be used for. The wire in the picture was deployed on the perimeter of an American firebase in Vietnam and I hope that it was the photo the person was going for because it looks painful, but it is sort of a cool shot.