After Spanish Civil War and with the uncertain evolution of World War II in Europe, the new Spanish fascist government decided to create a defensive line along the Pyrenees to prevent a potential invasion into the peninsula.
Between 1944 and 1957 the new regime invested a disconcertingly exaggerated investment of resources in the creation of a defensive line that, even without emulating Maginot or Sigfrid lines, European relics of the First World War during the so-called trench war, endowed the Pyrenean border with an infrastructure of more than five thousand fortified positions that has remained intact until today.
In fact the original project contemplated the construction of up to ten thousand bunkers and other types of fortifications that, although connected visually between them and grouped in resistance centres, covered almost completely the border with France between the Bay of Biscay and the Mediterranean. The project, designed by General Rafael García Valiño, then Army Chief of Staff, was called the P Line or Pyrenees Line, although it was also known as Perez or Gutierrez Line, probably by the surnames of military engineers who participated in the project. The creation of the defensive structure was due more to the fear of an Allied invasion against the Franco regime than to a German intervention willing to involve it alongside Axis forces. Of course, the existence of residual Republican troops who had crossed the border after the defeat or guerrilla contingents who resisted in the mountains was not considered a dangerous enough threat to justify such a deployment.
Retired Colonel Arcadio del Pozo considered that the purpose of the line was to avoid any enemy of the north the possibility of entering Spain. This enemy of the north would have had to prepare a numerous army, a powerful army and to spend a lot of efforts penetrating by any of the points of the line. In fact the original design barely completed the not worthless half project: more than five thousand strongholds which in some areas of difficult defence considered the cession of territory to the enemy.
Four different types of fortifications were erected, which were generally constructed in concrete using formwork and attempting to exploit, when possible, the orography of the terrain, even by digging into the rock some positions to reinforce the camouflage. In Puigcerda municipal archives there are still documents that testify the passage of twelve thousand men who along seven years participated in the works closest to the place. It is said that they were payed daily with a peseta, a sandwich and a glass of wine plus two weekly packets of cigarettes.
The most numerous constructions correspond to the nests of machine guns that require smaller space and that cover a wide shooting angle; the windows were covered of wood to avoid the rebound of the bullets. The artillery positions required logically larger dimensions, usually having a large room with the window suitable for heavy artillery, another room to store the ammunition and equipment and, in some cases were conditioned to accommodate, also, a garrison that, sometimes could reach twenty men. Another kind of artillery position had no deck and was designed to install antiaircraft artillery or mortar pieces. In some of them still can be seen the guides designed to displace the armament. One last type of bunker was dedicated to observation and communication posts. For these, elevated points were favoured with a wide line of sight, such as the Roc de l'Aliga - Eagle Rock -, in Musser, Girona Pyrenees, from where the route along Segre River is clearly dominated beside the town of Martinet. The situation of the positions guaranteed that crossfire could be carried out between them. Others, closer each other, are communicated through galleries and underground corridors, multiplying the firing points.
The garrisons that were to occupy the fortifications, in a case of necessity that never arrived - perhaps exceptionally during some military exercise -, were quartered in Figueres, Jaca and Pamplona and in some smaller mountain barracks.
In 1953 Luis García Berlanga film Bienvenido Mister Marshall – Welcome Mr Marshall - was premiered in Spanish cinemas. It was a reflection of the first American economic aid to the dictator's regime in 1951 and of the Madrid Covenants of 1953 by which the government ceded four military bases to the United States in exchange for economic and military support. The foreign enemy had disappeared and, as in June 1996, the then retired general José Luis Aramburu Topete recognized: Se siguió un poco por inercia pero ya se vio que no iba a servir para nada y conforme la política europea fue progresando pues en absoluto y por eso actualmente no tiene ningún valor. (It was followed a little bit by inertia but it was already seen that it was going to be unuseful and as the European policy was progressing at all and so it currently has no value).
In spite of their disuse the bunkers have been conserved in very good conditions in spite of the advance of the weed. In some cases they have been used as firewood or agriculture tools. More recently others, such as Coll de Banyuls, in Serra de les Alberes, near the end of the Pyrenees, have been adapted as huts for hikers, in others, such as those near Martinet in Cerdanya, to be visited and explain their history.