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Barbed wire is a type of fencing wire constructed with sharp edges or points arranged at intervals along the strand(s). It is used to construct inexpensive fences. A person or animal trying to pass through a barbed-wire fence will suffer discomfort and possibly injury. Barbed-wire fencing requires only fenceposts, wire and fixing devices such as staples. It is simple to construct and quick to erect by a skilled fencer.
Barbed wire was invented by Joseph F. Glidden of DeKalb, Illinois in 1873. It was an improvement on the less successful pointed wire products invented in 1867-68.
Patent Drawing for Joseph F. Glidden's Improvement to Barbed Wire, 11/24/1874. Barbed wire was the first wire technology capable of restraining cattle. Wire fences were cheaper to erect than their alternatives and when they became widely available in the late 19th century in the United States they made it affordable to fence much bigger areas than before. They made intensive animal husbandry practical on a much larger scale.
In the American Southwest
In the American Southwest barbed-wire fencing led to disputes known as the range wars between free-range ranchers and farmers in the late 19th century. These were similar to the disputes which resulted from enclosure laws in England in the early 18th century. These disputes were decisively settled in favor of the farmers, and heavy penalities were instituted for cutting the wire in a barbed-wire fence.
Barbed-wire fences remain the standard fencing technology for enclosing cattle in most regions of the US, but not all countries. The wire is aligned under tension between heavy, braced, fence posts (strainer posts) and then held at the correct height by being attached to wooden posts and battens, or steel star posts. The gaps between star posts vary depending on terrain—on short fences in hilly country they may be placed as closely as every 3 metres, whereas in flat terrain with long spans and relatively few stock they may be spaced out up to 30 to 50 metres. Wooden posts are normally spaced at 10 metres in any case with 4 or 5 batterns in between.
 Barbed wire fence in west Texas Agricultural fencing
Barbed wire for agricultural fencing is typically available in two varieties—"soft" or mild-steel wire and "high tensile". Both types are galvanised for long life. High-tensile wire is made with thinner but higher-strength steel. Its greater strength make fences longer-lasting because cattle cannot stretch and loosen it. It copes with the expansions and contractions caused by heat and animal pressure by stretching and relaxing within wider elastic limits. It also supports longer spans, but because of its "springy" nature it is less easy, and somewhat dangerous, for inexperienced fencers. Soft wire is much easier to work but is less durable and only suitable for short spans.
In high soil-fertility areas where dairy cattle are used in great numbers 5- or 7-wire fences are common as the main boundary and internal dividing fences. On sheep farms 7-wire fences are common with the second (from bottom) to fifth wire being plain wire. In New Zealand wire fences have to be easy to get through by dogs because they are the main means of controlling and driving animals on farms.
 Fence with barbed wire on top Human-proof fencing
Most barbed-wire fences, while sufficient to discourage cattle, are passable by humans who can simply climb over the fence—or through the fence by stretching the gaps between the wires using non-barbed sections of the wire as handholds. To prevent humans crossing, many prisons and other high-security installations construct fences with razor wire, a variant which instead of occasional barbs features near-continuous cutting surfaces sufficient to severely injure anyone who climbs on or over it.
Barbed wire is also used in war. Much of the artillery bombardment on the Western Front in World War I was aimed at cutting the barbed wire that was a major feature of trench warfare. The wire was not designed to stop the passage of men, just to impede them long enough to be possible to kill them with machine guns.
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