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 in the Iberian System ranges to the north and northeast of Valencia. The defenses were built to withstand bombardment by either heavy artillery or 1,000-pound aerial bombs. Background Following the success of the Aragon Offensive resulting in the Nationalist armies reaching the Mediterranean Sea, the Republic was split in two; the Spanish Republican Army was in disarray and the road to Barcelona was open for conquest by the Nationalists. Even General Vicente Rojo Lluch said that Barcelona could have been taken with "less force and in less time" than in January 1939. The Nationalist generals and Francisco Franco's German and Italian allies expected a swift attack against Barcelona. Nevertheless, Franco decided to turn south against the capital of the Spanish Republic at Valencia for fear of French intervention in Catalonia, following the Anschluss. Furthermore, he did not want a swift end to the war but a war of annihilation against the Republic to crush all opposition. Dionisio Ridruejo said, "A long war meant total victory. Franco chose the crueller option which, from his point of view, was also more effective." Nationalist offensive The Nationalist offensive started on 25 April, with General José Enrique Varela's Army Corps of Castille, Antonio Aranda's Galician corps, and Garcia Valiño's formation, but the advance was halted on 27 April. On 1 May, the Nationalists continued their offensive, advancing on three fronts from Teruel (Varela), the Mediterranean sea coast (Aranda), and a central column moving between them through the mountains (Garcia Valiño). The Nationalists found it slow going due to rainy weather in March and April that slowed the offensive, the difficult terrain that aided the defense of Republican forces being driven back before them, and the dogged determination of the Republican troops, reinforced with new weapons brought in from France: Soviet Supermosca (I-16 Type 10) fighters with four machine-guns, 40 Grumman FF fighters and anti-aircraft guns. On June 13, Castellón fell