The defensive points of the Línea P and its access roads were built by war prisoners and jailed political opponents of the Francoist regime grouped in Batallones de Trabajadores (Workers’ Battalions) immediately after the Spanish Civil War and from 1940 to December 1942, in Batallones Disciplinarios de Soldados Trabajadores (Disciplinary Battalions of Workers-Soldiers) In a broader sense, Línea P also refers to the successive Pyrenean fortifications built after the Spanish Civil War that would previous fortifications (1939–1940), the counter-tank defense (1950–1954) and other fortifications, such as those at Cape Higuer in Fuenterrabía, Guipúzcoa finished in 1957.

[3] After the end of the Spanish Civil War, hundreds of thousands of Republican soldiers and civilians crossed the French border ahead of the advancing Nationalist troops.

Beginning 1943, Nazi Germany started to build a line of fortifications in the Pyrenees, called Sperrlinie Pyrenäenfront, from Cerbere to Hendaye, along Le Perthus, Maurellàs, Las Illas, Prats-de-Mollo-la-Preste and the French Cerdagne and built coastal batteries in Le Barcarès, Torreilles, Sainte-Marie-la-Mer, Collioure et Port-Vendres which became part of the Südwall.

Neither General Franco nor Nazi Germany could ever manage to close the border effectively, as alternative routes to the usual ones were sought to cross it.

[9][10][11] The exiled Republicans had high hopes that at the end of World War II in Europe, Franco would be removed from power by the victorious Allies and that they would be able to return to Spain.

The objective of the offensive was to retake the sector of Spanish territory comprising the land between the Cinca and Segre Rivers and the French border.

The zone was later declared conquered by the Spanish Republican government in exile to provoke a general uprising against Franco throughout Spain.

[21] The invasion of the Val d'Aran ended on 28 October 1944 in a complete failure for the Republican side,[21] when the last guerrillas re-crossed the border back into France, without the hoped-for uprising.

[22][23] In an attempt to isolate the Franco regime, Félix Gouin, de Gaulle's successor as head of the French provisional government, decided on 26 February 1946 to close the border with Spain on 1 March 1946.

[20][24] On April 18, 1946, Polish ambassador Oskar Lange, supported by the Soviet Union, France and Mexico, asked the United Nations to condemn Spain as an aggressive country based on information that Franco was accumulating troops on the French border and fortifying the Pyrenees, but nobody knew that these works had already begun in 1939 earlier in the whole mountain range.

[27][28][29][30] On December 12, 1946, the UN General Assembly adopted Resolution 39, which excluded the Spanish government from international organizations and conferences established by the United Nations.

On 4 November 1950, the UN General Assembly adopted resolution 386, repealing the recommendation that prevented Spain from being a member of the International agencies established or linked by the United Nations.

In 1936, months before the Civil war, cavalry commander Sanjuán Cañete published a book on the Pyrenean border giving indications of possible defensive works to be done.

[37] More specifically Sanjuán Cañete carried out a detailed analysis of the network of trails and roads on the Pyrenees, adding considerations and proposals of a strategic nature.

[37][38] Since September 1940 there had been plans to fortify the Eastern Pyrenees (Catalonia) in the event of a possible invasion through Le Perthus with motorized troops.

[27] Started in the autumn of 1944, the construction of the Línea P was entrusted to the former military regions IV ( Catalonia and Valencia), V (Aragón and Soria) and VI (Navarra, País Vasco, Santander, Burgos, and Logroño) that bordered France.

This centers of resistance were intended to cover the main lines of penetrations, inside Spanish territory, while capable of defending themselves autonomously.

Spanish military strategists needed also to compensate for the defensive weaknesses of the two extremities of the Pyrenees: the Basque Country and Navarra in the west and Catalonia in the east.

The Francoist project for the 500-km fortified line across the Pyrenees consisted of some 8,000 – 10,000 defensive points of which approximately half were built, stretching up to a depth of 60 km (37 miles) from the border.

In spite of the effort made in its construction, there is no evidence that it was ever fully operational and armed, nor the armored doors that were manufactured to close the bunkers were placed or the barbed wire fences were deployed.

[4] The wire fences and armored doors that were produced to protect these settlements remained in storage in Figueras, Pamplona, and Jaca and eventually sent to the Spanish Sahara.

[53][55] The integration of Spain into the then European Economic Community and NATO in 1986 lead to the definitive abandonment of the Pyrenean fortification line as a defensive military infrastructure, becoming, in some cases, another tourist attraction in the Pyrenees.

When the Third Carlist War ended in 1876, the Spanish military authorities came with an ambitious plan to defend the French border in the central and western Pyrenees.

[56] Around Irun, a group of defensive forts was proposed and the construction of the Campo Atrincherado de Oyarzun (Entrenched camp at Oiartzun) started.

The region of Cerdanya was considered of high strategic value and therefore concentrated a large number of defensive points and bunkers built to stop an intrusion at one of the most important penetration routes through the Pyrenees.

111 was made up of 13 fortified defensive points located in the southern area of the Paseo de los Melancólicos in Canfranc.

[77][78] The route starts from the low battery of the fort of Santa Elena and some settlements belonging to the Center of Resistance 106 (Hoz de Jaca) can be visited.