The Castle of Mytilene (modern Mytilini), encompassing an area of 200,000 m2 (20 hectares), is considered one of the largest fortresses in the Mediterranean. Excavations by the Canadian Institute have uncovered the sanctuary of Demeter, proof that the site has been inhabited since antiquity. The first Byzantine phase of the fortress is estimated to date to the reign of Justinian (6th c. AD). The present form of the castle is the result of the building activity of the Gattelusi, who ruled the island during the Late Byzantine period (1355-1462), and above all the Ottomans, who occupied Lesbos from 1462 until 1912. It is divided into three parts in accordance with its overall configuration: the Upper, Middle and Lower Castle. The Upper Castle The Upper Castle forms the main fortification enclosure. Access is via the main double gate on its southern side. The castle’s most important administrative and religious buildings were located here. The Large Enclosure. This was the Castle’s most heavily-fortified point. It included five towers that defined an open rectangular space. On the central western tower known as the “Queen’s Tower”, there is a dedicatory plaque with the Gattelusi coat-of-arms, as well as the eagle and the four Bs of the Byzantine Palaiologans. This was the rulers’ residence. The Koulé Mosque, which today lies in ruins, was one of the two mosques that were once in the castle. It preserves its ascending staircase leading to the gallery and its mihrab (prayer niche). It was built atop a Christian church dating to the period of the Gattelusi that was dedicated to Agios Ioannis (Saint John). The Middle Castle The Ottoman gate, Orta Kapu (= the Middle Gate), dating to 1373, leads to the Middle Castle. The following monuments are preserved from the Middle Castle: The Powder Magazine. This was an Ottoman building constructed for ammunition storage. To protect the building from fire, the upper floor was of stone, and for security reasons it was surrounded by a high wall. The Madrassa, the Ottoman theological school. This two-storey building, which was square in plan, was organized around a central atrium. On the upper floor there were classrooms and rooms for prayer, as well as cells. The kitchen, dining-area and storerooms were on the ground floor. The Tekke, the Ottoman monastery where Ottoman monks resided. It was a small, domed building. The Military Hospital – Prison. This was an Ottoman building used as an army hospital and prison. It was an one-storey building, but also had basement spaces that were used as holding cells. The Cistern, one of the fortress most important buildings, with a capacity of 400 m3 (=14,126 cubic feet) of water. It occupied the site of a Roman public building and multiple building phases may be discerned. Its roof was constructed in such a way as to collect rain water. The Fountain, an Ottoman building. There was a cistern at its rear. The Lower Castle In 1644, Ibrahim Han proceeded to create the Lower Castle to protect the north harbor and its connection with the Middle Castle, with which it communicated via the Byzantine postern gate. On its northern side there was an Ottoman gate that was demolished in 1960 to allow for vehicular traffic. There were around 80 houses in this area. Today, the Ottoman bath-hamam, the Ottoman fountain, eleven houses, and the chapel of Panagia Galousa remain.