In 1256, the title of main church of the town was conferred to this church. To access to it there is a staircase that was built in the 20th century, at the beginning of the seventies. It gives to the church not only an upward aspect, being in a high position, but also the tower adds verticality.

The façade dates from the first half of the 13th century; it shows a clear Arabic influence, although it has also some Romanic decorations in a vegetable, geometric and figurative lace (with a harpy, a mermaid, a centaur and two griffins).

The church’s interior presents constructive forms with an origin in the last quarter of the 12th century. From this period is the head of the temple formed by three apses, which stair, was created in 1893 by a stonemason from Estella Cayetano Echauri. The church is formed by three naves. In the Gospel nave is the San Andres chapel built in 1696 with an altarpiece from the second half of the 18th century. The temple has a St. Peter’s image of 1687 in a preeminent position. It presents pictures like the “O” Virgin (14th century) or Rosario Virgin, art of the first half of the 17th century. It has a beautiful baptismal font dated in 12th century.

There is a splendid cloister built in 1170. Two sides were destroyed in 1572 as a consequence of the castle´s destruction. About the sculpture quality, the capitals were carved by different artists’ hands. In the north side the capitals show the life of saints, fighters, tamers & sphinxes, and on the west side there is a bestiary with mermaids, harpies, griffins and vegetal decoration.