Quadrangular castleWhile constructing defensive fortifications in Baku, great towers have been built as an integral part of the castle walls in order to protect firmness and magnificence of walls and facilitate the defence system. According to medieval authors, there were 70 semi-circular towers and one tetragonal castle-typed tower within northern castle walls in Baku. In the Middle Ages, the castle has been used as a weapons depot both in the period of peace and war. The construction of the castle tower was majorly aimed for two purposes. To control the area in order to further strengthen the defence of Baku city in the northern side by increasing the magnificence of castle walls and use the vast fortress space as a weapons depot. This four-cornered castle was named Donjon. "Donjon" is a French word which is translated as a bastion of defence.In 2014, the monument has been thoroughly repaired by the "Old City" State Historical-Architectural Reserve Department and afterwards started to be operating as the Old City Traditional Arts Center under the name of Art Tower.