The XYZ Line, or Matallana Line, was a system of fortifications built during the Spanish Civil War in order to defend the capital of the Second Spanish Republic in Valencia, Spain. Unlike the Maginot Line, or the Iron Belt ("Cinturón de Hierro") of Bilbao, which were expensive systems of fortifications and bunkers made of reinforced concrete, the XYZ Line was a simpler system of defenses in depth consisting of trenches and bunkers that took advantage of some of the most difficult terrain in Spain to the north and northeast of Valencia. The defenses were built to withstand bombardment by either heavy artillery or 1,000-pound aerial bombs.