Answer: Sevilla - The Torre del Oro is a military watchtower that was built in 1220-1221 on the banks of the River Guadalquivir. The tower is 36 metres highs. Although some people believe that it was called the "Gold Tower" because it was built with the gold brought back from the Spanish conquest of the Americas, or that gold was stored here, it is more likely to be because of the gold reflection of the tower dome on the river.