Mudéjar

Mudéjar, coming from the Arabic word Mudajjan meaning "domesticated", is used to reference the Muslims who remained in Spain after the Christian Inquisition. They weren't converted to Christianity and were protected by the Treaty of Granada(1491) to have religious and cultural freedoms. The style that developed through the relationship of the Christians, Muslims, and Jews during this time is identified as symbiotic.

The Mudéjar style emerged in the 12th century on the Iberian peninsula and survived all the way into the 17th century. The style was strongly characterized by the use of brick as the main material. Instead of involving new geometries or architectural elements, it reinterpreted cultural styles with the use of Islamic influences. The Mudéjar style also consisted of complex tile patterns. These patterns were meant to give life to flat surfaces on either walls or floors.

Mudéjar pattern on tile

The horseshoe arch was another one of the elements that was a strong indicator of Islamic influence. Before the Muslims invades Spain, the horseshoe arch was a main architectural feature for the Visigoths. From them, the Umayyads took the form, and accentuated the curvature of the arch through the alteration of colors.

Horseshoe arch in the Mosque of Cordoba

Sources:

http://en.wikipedia.org/wiki/Mud%C3%A9jar
http://journal.utarts.com/articles.php?id=14&type=paper
http://en.wikipedia.org/wiki/Horseshoe_arch