The Pillau Fortress is a fort-citadel in the city of Baltiysk, for many centuries the main defensive structure of the city of Pillau in East Prussia.
The construction of the fortress began in 1626 by the Swedes, and it was completed by 1670 by the residents of Prussia. In 1697, Peter the Great visited the fortress, where he studied military and fortification affairs.
During the Second World War, the Pillau Fortress was the most important stronghold of the German troops in East Prussia. Soviet troops took the fortress on the night of April 26, 1945.