The "Giralda Tower" was originally a "Minaret", part of the Moorish Mosque that preceded the Cathedral. In 1248 the Minaret was considered a marvel even to Fernando III who demanded its protection prior to him conquering the city.
The construction of the Tower (Minaret) was ordered by the Almohad ruler Yousouf Yacoub al-Mansour.
Construction was started on "La Giralda" in 1184 and lasted for twelve years. When completed in 1196 the top of the tower didn't look like it does today. It was used to call Moors to prayer and also as an astronomical observatory. In 1198 four brightly polished copper spheres were added by the Moors to the top of the tower. The reflecting sun light from the balls was so brilliant the city made its presents known for miles. When the copper spheres were destroyed by an earthquake in 1356 they were replaced (in 1400 AD) by Christian religious features (cross and bell). The present bell room at the top was added to the tower in 1560, with construction ending in 1568AD.