is the altar from El Perú (Maya site), which features a quatrefoil on the back of a zoomorphic creature in which sits a ruler. The associated hieroglyphic text refers to the creation narrative of the Maize god's rebirth. Barbed quatrefoil The barbed quatrefoil is a quatrefoil pierced at the angles by the points of an inscribed square, which gives an image akin to an heraldic rose, which is termed "barbed" due to the stylised thorns which project at the intersection of each pair of petals. The earliest example of the barbed quatrefoil appears on the south transept buttresses of 1260 in the Cathedral of Notre Dame in Paris. Similarly, the trefoil is often combined with an equilateral triangle to form a barbed trefoil. Among the most famous works of art employing the barbed quatrefoil are the bronze panels on the south doors of the Florence Baptistery (1330–36) by Andrea Pisano, the bronze panels of the north doors of the Florence Baptistery by Lorenzo Ghiberti, Filippo Brunelleschi's competition entry for the same doors (The Sacrifice of Isaac), as well as Head of an Angel by Piero della Francesca. In heraldry In heraldic terminology, a quatrefoil is a representation of a four-leaf clover, a rare variant of the trefoil or three-leaf clover. It is sometimes shown "slipped", i.e. with an attached stalk. In archaic English it is called a caterfoil, or variant spellings thereof. A double quatrefoil (or octofoil) is the mark of cadency for a ninth son in the English heraldic system. In the military The quatrefoil is mainly used in ecclesiastical buildings, primarily for windows, but Clifford’s Tower in York Castle is built in the shape of four overlapping towers, like a four leaf clover and is also known as a quatrefoil. In the U.S. Marine Corps, quatrefoil refers to a four-pointed decoration on the top of a warrant or commissioned Marine officer's dress and service caps (see peaked caps, also known in the Marines as "barracks covers"). According to tradition, the design was first used with Marine officers on sailing ships so that Marine sharpshooters in the rigging did not shoot their own officers on the deck during close-quarters gun battles (as when crews of opposing ships attempted to board each other's ship). An official part of U.S. Marine Corps officer uniforms since 1859, the quatrefoil was said initially to have been crossed pieces of rope sewed into officers'