The Tena Valley, due to its proximity to the neighbouring country, France, has had the mission of protecting the rest of the country from possible invasions. That is why throughout its villages you can see different fortifications, such as castles from the 15th-16th centuries, forts and recent 20th century bunkers.
The most recent fortifications are those belonging to the P Line or Line of the Pyrenees. Commissioned by General Franco after the end of the Spanish Civil War, it is the largest defensive structure built in Europe after the Second World War (autumn 1944), as it covers the entire Pyrenees mountain range, from the Bay of Biscay to the Mediterranean. It is also Spain's largest military engineering work, the purpose of which was to seal the border with France to protect against a possible invasion through the Pyrenees. This work was never completed and never entered into service.
In Aragon, line P is divided into 5 sectors and each one into resistance nuclei (N.R.), in the area of Sallent de Gállego there are N.R. 108, 109 and 110.