The citadel of Ioannina (Kastro) is an irregular trapezoid-shaped fortress built on a rocky headland on the western shore of Lake Pamvotida. The present form of the citadel is the result of extensive construction by Ali Pasha in the late 18th and early 19th century, in many places incorporating the existing Byzantine fortifications. At the beginning of the 19th century a new fortified wall was constructed outside the Byzantine fortification, primarily on the western side, and the gap between the old and new walls was bridges with transverse barrel-vaults, forming a sequence of vaulted structures. The central gate was located along this wall. There were bastions along the walls and a walkway on top. A moat ringed the fortress, filled with water from the lake (the moat's course is now followed by Karamanli and Ethnikis Antistaseos streets).