It was built to replace the old Romanesque shrine of San Blas. The church has a single nave with chapels between the buttresses and a five-sided sanctuary. The cathedral interior is covered with ogive and pointed barrel-vaulted ceilings. The side names were added in the 15th century and the chapels were opened in the 16th, 17th and 18th centuries. One of the highlights of this monument is its magnificent octagonal brick tower, both the exterior and interior). Other elements of note include the north facade in the Gothic style and the main altar piece in gilded and polychrome wood, the Renaissance sculptor Damián Forment in 1515 and featuring the image of Saint Paul. This is a prime example of the Mudejar architecture of Aragon, awarded the World Heritage Designation by the UNESCO.