The cheval de frise (plural: chevaux de frise [ʃə.vo də fʁiz], "Frisian horses") was a medieval defensive anti-cavalry measure consisting of a portable frame (sometimes just a simple log) covered with many projecting long iron or wooden spikes or 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 the Civil War, the Confederates used this type of barrier more often than the Union forces. During World War I, armies used chevaux de frise to temporarily plug gaps in barbed wire. Barbed wire chevaux de frise were used in jungle fighting on south Pacific islands during World War II.
French: Cheval de frise literally means "Frisian horse". The Frisians, having few cavalry, relied heavily on such anti-cavalry obstacles in warfare. The Dutch also adopted use of the defensive device when at war with Spain. The term came to be used for any spiked obstacle, such as broken glass embedded in mortar on the top of a wall.
The cheval de frise was adapted in New York and Pennsylvania during the American Revolutionary War as a defensive measure installed in rivers to prevent upriver movement by enemy ships.
During the American Revolutionary War, Robert Erskine designed an anti-ship version of the cheval-de-frise to prevent British warships from proceeding up the Hudson River. A cheval-de-frise was placed between Fort Washington at northern Manhattan and Fort Lee in New Jersey in 1776. The following year construction began on another one to the north of West Point at Pollepel Island, but it was overshadowed by completion of The Great Chain across the Hudson in 1778, which was used through 1782.
Similar devices planned by Ben Franklin were used in the Delaware River near Philadelphia, between Fort Mifflin and Fort Mercer. A line of cheaveaux-de-fris were placed across the Delaware River at Marcus Hook as a first line of defense for Philadelphia against the British naval forces.
A cheval-de-frise was retrieved from the Delaware River in Philadelphia on November 13, 2007 in excellent condition, after more than two centuries in the river. In November 2012, a 29-foot (9 m) spike from a cheval-de-frise was recovered from the Delaware off Bristol Township; it was also believed to be from the Revolutionary era installation at Philadelphia and freed up by Hurricane Sandy earlier that fall.