cheval-de-frise

noun pl. chevaux-de-frise chevaux′·-de-frise′ (s̸hə vō′-)

1. an obstacle, usually a piece of wood with projecting spikes, formerly used to hinder enemy horsemen
2. a row of spikes or jagged glass set into the masonry on top of a wall to prevent escape or trespassing

Etymology: Fr < cheval, a horse + de, of + Frise, Friesland: first used by Frisians, who lacked cavalry, against Spaniards