The dodecagonal Torre del Oro was built by the Alhmohad dynasty as a watchtower on the Guadalquivir. It was built under the orders of Abu-l-Ulà Idrís al-Mamun. It is widely believed that an additional 8 meters were added to the tower in the fourteenth century. The third level, including the circular portion, was added in 1760 by the engineer Sebastian Van der Borcht after the tower sustained damage in the 1755 Lisbon earthquake.