The 13th century Gold Tower , or “Torre del Oro” in Spanish, was originally a military watchtower, carefully controlling who entered and left the city via the river Guadalquivir with a thick chain stretching across the base of the river. The tower has become a monument of great importance which was once used as a prison in the middle ages and is used nowadays as a naval museum depicting the naval history of Seville through documents, engravings and models. The tower most probably gets its name from the golden tiles which cover its dome and which maybe once covered the whole body of the tower.