The historical heritage of Sanlúcar is to a large extend defined by its relations to America. From here Columbus started his second voyage to America. Many buildings are from this period, like the Iglesia de Santo Domingo (16th c.) or the Iglesia de la Merced (17th c.). Older is the Iglesia de Ntra. Sra. de la O (14th c.) with a panelled ceiling in the Mudéjar style, the Castillo de Santiago (15th c.), which protected the mouth of the Guadalquivir against pirate attacks, or the palace of the dukes of Medina Sidonia (15th c.), whose dominion Sanlúcar belonged to.