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Cheval de frise at the Confederate defenses at the Siege of Petersburg

The cheval de frise (plural: chevaux de frise) was a Mediaeval defensive obstacle consisting of a portable frame (sometimes just a simple log) covered with many long iron or wooden spikes or even actual spears. They were principally intended as an anti-cavalry obstacle but could also be moved quickly to help block a breach in another barrier. They remained in occasional use until they were replaced by wire obstacles just after the American Civil War, during which it was most often used by the Confederates.^[1]

Cheval de frise according to the later use of the term, broken glass studding the top of a wall in a nineteenth century fort

French: Cheval de frise means "Frisian horse". The Frisians, having little cavalry of their own, relied heavily on such anti-cavalry obstacles. The term also came to be used for any spiked obstacle, such as broken glass embedded in mortar on the top of a wall.

A variation of the chevaux de frise are Czech hedgehog anti-tank obstacles, typically composed of three rails, crossed in such a way that they form a six-spiked figure, possibly sealed in concrete or partly buried in sand or earth (very much like a metal abatis). They can also be mined. The Atlantic Wall used millions of such obstacles to slow down landing of armored and mechanized troops, as to make them easy targets for machine guns and coastal artillery.

An anti-ship version was designed by Robert Erskine as a means of keeping British warships out of the Hudson River during the American Revolutionary War. The device was never deployed in the Hudson, but similar devices planned by Ben Franklin were used in the Delaware River near Philadelphia, in between Fort Mifflin and Fort Mercer.^[2] A cheval-de-frise was retrieved from the Delaware River in Philadelphia on Nov 13, 2007 in excellent condition, after more than two centuries in the river.^[3]

The "knife rest" or "Spanish rider" is a modern wire obstacle functionally similar to the cheval-de-frise, and sometimes called that.