Not only is this magnificent building the most important cathedral in Spain, but it also includes four museums and houses a valuable art collection. Now a great Christian temple, the cathedral was built on the site of the main Muslim mosque and of two earlier, Visigoth, churches. The tower is unique, each of its doors has its own individual character, and the façade and interior exhibit a number of different architectural styles making the monument a veritable showcase of extraordinary historic and artistic value. Paintings by El Greco and Titian and gems like the magnificent processional monstrance, which plays a leading role every year in the city's celebration of Corpus Christi, are complemented by the internationally famous Transparente, an architectural detail conceived and executed by Narciso Tome in marble, jasper and bronze.