The powerful and imposing fortifications of the Citadel, by the Jaffa Gate entrance, are crowned by crenellated walls, towers, and the distinctive cylindrical minaret improperly known as the Tower of David (pbuh), which is actually a minaret of a mosque built in the Ottoman period
The Citadel is the result of construction work done at the time of the Mamluks in 14th century by King Ibn Qalawoon who added a mosque in 1310 and fortified it, and of later alterations during the time of Suleiman the Magnificent who added another minaret to the mosque in 1531.
However, in a more ancient past, at least as far back as the time of Herod the Great, there already existed a citadel of which interesting vestiges remain. In 24 BC Herod had three towers built, to which he gave the names of the people closest to him: his brother Phasael, his wife Mariamne and his friend Hippicus. In reality, these structures were the answer to the necessity for solid defense works to protect the adjoining palace.
At the time of the Roman conquest, the Emperor Titus spared the towers from destruction and converted them into lodgings for the Tenth legion. The Byzantines reconstructed the fortifications, and Muslims enlarged the Citadel. The Mamluks expanded it in the 14th Century and the Ottomans gave it is present appearance.
The Museum of the History of Jerusalem has been set up in the interior, while the sound-and-light shows are held in the enchanted atmosphere of its fairy-tale setting.
from http://www.atlastours.net