Barbed wire

A type of wire constructed with sharp edges or points designed such that a person or other animal trying to pass through the fence will suffer discomfort (or possibly injury).

Barbed wire was the first wire technology capable of restraining cattle, and with the relative ease with which wire fences can be erected, when it became widely available in the 1850's (?) in the United States it made possible the fencing of much bigger areas than previously feasible, and thus made practical intensive animal husbandry on a much larger scale.

Barbed wire fences remain the standard fencing technology for cattle in most regions. The wire is suspended under tension between heavy, braced, fence posts, and then aligned by being attached to 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 relatively few stock they may be spaced out up to 30-50 metres.

Barbed wire for agricultural fencing is typically available in two varieties - "soft" wire and "high tensile". High-tensire wire is made with thinner, but higher-strength and more elastic steel. Its greater elasticity make its fences longer-lasting (as they cope with the expansions and contractions caused by heat and animal pressure by stretching and relaxing within their elastic limits) and supports longer spans, but because of its "springy" nature is unpleasant and somewhat dangerous to work with for inexperienced fencers. Soft wire is much easier to work with, but is less durable and only suitable for soft spans.

Most barbed wire fences, while sufficient to discourage cattle, are passable by humans who can simply climb through the fence by stretching the gaps between the wires, using non-barbed sections of the wire as handholds. For preventing human 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 over it.