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Dominating the eastern end of Plaza del Pilar, La Seo was built between the 12th and 17th centuries and displays a fabulous spread of architectural styles from Romanesque to baroque. The cathedral stands on the site of Islamic Zaragoza's main mosque (which in turn stood upon the temple of the Roman forum). The admission price includes entry to La Seo's Museo de Tapices, a collection of 14th- to 17th-century Flemish and French tapestries considered the best of its kind in the world.

The church's northwest facade is a Mudéjar masterpiece, deploying classic dark brickwork and colourful ceramic decoration in complex geometric patterns.The cathedral is also Zaragoza's finest example of Christian architecture: all the chapels are framed by beautiful stonework and ring the changes from the eerie solemnity of the Capilla de San Marcos to the glorious Renaissance facade of the central Christ Chapel and the exquisite 15th-century alabaster high altarpiece.