The village, which was the capital of the old Kingdom of Sobrarbe, and was later incorporated into the Kingdom of Aragon in the 11th century, constitutes a magnificent example of medieval urban development.

The historic quarter of the village of Ainsa, declared a Historic-Artistic site, is formed by a group of houses that are packed together in the most harmonious and uniform of ways, among which the slender tower of the collegiate church stands out, as well as the enormous premises of the castle, almost as big as the rest of the town. The walls that surrounded the town centuries ago remain almost intact today, the town itself being filled with monuments that bring us back to the Middle Ages.

Adjacent to the square, with porches lining it on both sides, we have the Romanesque church of Santa Maria, from the first half of the 11th century. There, we can admire its main front, and interesting crypt, and the tower, which dominates the whole town. The cloister was built some time later, during the 13th century.

To the north-east of the city centre we find the citadel. Its origins date back to a pentagonal tower from the 11th century, which was incorporated into the defensive system, in the face of the danger posed by the Muslims. Towards the end of the 16th century, this fortress was renewed by the construction of the present citadel, as part of the defensive system at the French border.

To commemorate the Reconquest of this village, a street play with the theme of Moors and Christians is staged, called "La Morisma".