Stock Photo - Jaca Citadel had been called the San Pedro Saint Peter Castle until the 19th century. It was built from 1595 until the late 17th century, to secure the frontier with France and to prevent the Huguenot army from entering Spain through the Santiago pilgrimage route. The castle was designed by the Italian Knight Commander Tiburcio Spanich in the shape of a pentagon with a turret made of stone ashlars at each angle. The citadel is surrounded by a defensive wall, a dry moat and a glacis. Inside the citadel is a courtyard, surrounded by walls with machicolations. The castle is the only military construction of its kind in Spain to survive completely intact. It was declared a National Monument in 1951.