The machines that manufacture it are not particularly big - roughly the size of a small sedan. On the web you can watch them in action, looking a bit like a crazed Victorian era steam engine, with spinning cogs pulling a double strand of wire of a spool while a mechanism on feeds in short sections to make the barbs. Another twist traps the nasty shards into the body of the wire while another spool takes up the finished product.

On one level, it's a clever though slightly dizzying process to watch. On another, it is another triumph of modern industry that begins with the mining and production of steel.

Early wire was prone to snapping when cattle leaned on it. High tensile wire required advances in metallurgy, which includes the production of pig iron by removing impurities. The iron contains carbon to give it strength, though too little or too much makes it brittle.

The first fences appeared with the beginning of agriculture 10,000 years ago. The were made from wood, earth, stone and plants such as hedges in Europe, or cactus in South America.

Although short lengths of wire were first made at least 5000 years ago by hammering pliable metals such as gold, longer lengths of wire didn't appear until the year 1000. These were made by pulling rods of soft metal, such as alloys of lead and tin, through a die of harder metal such as iron.

Metal was not used for fencing until steel wire became available in the 19th century.

By 1870 steel wire could be produced large amounts of using improved steelmaking techniques.

In the USA, Michael Kelly made wire known as the "thorny fence" by twisting two wires to form a cable for barbs. In 1873, Joseph Glidden, a farmer from Illinois was issued one of the first patents for a simple wire barb locked onto a double-strand wire.

Since then, barbed wire has had a vast impact by enforcing private ownership of land and stock. It has limited the movement of wildlife and farm animals. Cattle herding has largely disappeared.

The lives of nomadic indigenous people were radically altered when they were squeezed further from their lands. In America, they called barbed wire "the Devil's rope".

Since then, barbed wire has become ubiquitous in security and in war, and anybody who's got themselves tangled in it, knows how effective it is.

Response by: Rod Taylor