The Church of St. Peter and the cloister of San Pedro are of Old Roman style. Its origins go back to the times of the mozárabes, although some authors claim that may have been constructed on the ruins of a Roman temple. After the reconquest of Huesca in 1096 settled in a denedictine community  in this temple.

The construction of the temple was extended along the twelfth and thirteenth centuries, was terminated when they completed the construction of the hexagonal tower which houses the chapel of St. Ponce. The floor of the temple is made up of three ships that were constructed at the same time of the cloister. His sculpted capitals show scenes from the Old Testament, along with mythological scenes, and rich elements of oriental imagery of the time. The old San Pedro was declared a National Monument in 1885 and is linked to the history of the Kings of Aragon.

In the same cloister is located the Chapel of St. Bartholomew, that is royal pantheon, as in the interior lie the remains of two Aragonese kings: Alfonso V the Warrior and Ramiro II the Monk. Tradition also relates the church of San Pedro with the legend of the Holy Grail, that some say was guarded at this temple for four centuries.