The Almohad rulers of Sevilla erected this tower and another just like it across the river in 1220 as a defensive mechanism. A stout chain linked the two, preventing ships from moving in and out of the port without authorization. The system proved fruitless when a Castillian admiral broke the chain during the 1248 siege. The complementary tower vanished centuries ago, but the Torre del Oro has stood for nearly 9 centuries, serving at various times as administrative offices and a warehouse. Its name derives from the unusual yellow-tinged plaster made of mortar, lime, and straw. These days it serves as the Museo Maritimo and recounts the history of port from its Almohad era to its shipping heyday of the 16th and 17th centuries.