The Quadrangular Mardakan Fortress or the Great Mardakan Castle is a historical and architectural monument located in the Mardakan settlement of the Khazar district in Baku. It is included by the Ministry of Culture and Tourism of Azerbaijan in the list of monuments of world importance. In 2001, along with other objects of the coastal defence of the Caspian Sea, it was included in the UNESCO World Heritage Reserve List.

Mərdəkan (Mardakan) is a settlement and municipality in Khazar raion of Baku, Azerbaijan with a population of 25,232. It's located on the eastern Absheron Peninsula only 30 km away from capital city Baku, bounded by the Caspian Sea to the north, Shuvalan to the east, Qala to the south, and Shagan to the west. Mardakan received the status of a settlement in 1936. In 1933, Shagan village was included in the Mardakan village council, although it was separated in 1945, it was reunited in 1948, and in 1990, Shagan re-separated and received the status of a settlement.