Château de Saint-Béat dates from the 12th century. It was enlarged by Henri IV (1553 – 1610). Rulers rarely lived in Saint-Béat; the castle was occupied by captains until the 16th century. In 1588, the Parlement of Toulouse passed a law that required the inhabitants of Melles, Argut and Arlos by turns to guard the castle, subject to a fine of 500 écus. The castle never had to repel invasions, though its strategic position close to the Spanish border led to it being described as 'la clef de France' (the key to France).
The castle was surrounded by two enceintes. The keep measures 5m square and had two storeys. The castle provides views over the village and the Garonne valley.
References:Bomarsund fortress and garrison was built in 1832-1854 by Russian Empire to defence Åland Islands against enemies. British and French fleet attacked against it during the Crimean War in 1854. After a week of fighting the British stormed the remaining fort. Anglo-French forces destroyed it totally after battle. In the Treaty of Paris 1856, the entire Åland Islands were demilitarized, which is a status that has been preserved until this day.
Nowadays there are some ruins left and fortress area is open for visitors.