A coil of barbed wire rests on a wood corner post. The weight and tension of a wire fence mean that corners need to be strongly reinforced to keep the fence from sagging or even collapsing.

Invented and first patented in 1867 by Lucien B. Smith of Kent, Ohio, barbed wire was subsequently modified by Joseph F. Glidden of DeKalb, Illinois, who is commonly -- but mistakenly -- called the inventor of this type of fencing.

Photo by Nova Development Corp. Used under license.