The cathedral stands on the site of the Great Mosque of the 12th century. Today, the only part which remains of this structure is the minaret, also known as the Giralda due to the weather vane added to the top in the 16th century. The Abluciones courtyard and today's Puerta del Perdón door are also parts of the old mosque. It was converted into a Christian church when the city was conquered by Ferdinand III of Castile in 1248. Several stages of building can be seen, with examples of the Mudéjar, Gothic, Renaissance, Baroque and Neo-classical styles. Access to the cathedral is through the Plaza Virgen de los Reyes square. It has five naves (the main nave has a height of 36 m.) and a rectangular ground plan, measuring 116 m. long and 76 m. wide. The transept rises to a maximum height of 40 m. The main altarpiece was built over a series of different periods, and includes pieces by the brothers Jorge Fernández Alemán and Alejo Fernández, Roque Balduque, Pedro Millán, Juan Bautista Vázquez the Elder and Pedro de Heredia. The Renaissance-style chapter room dates from the second half of the 16th century. The main sacristy is Plateresque. The remains of Christopher Columbus lie in the cathedral.