Because of its geographic position, Niš has historical monuments and sites dating from two thousand years ago to modern times. A few people know that Niš was birthplace of the Roman Emperor Constantine, famous for legalizing Christianity. Remains of his summer residence Mediana are preserved. From the Turkish era the Fortress remains the central landmark of Niš, while unique and chilling Skull Tower (1809) represents the barbarity of the Turkish occupation and bravery of the Serbian freedom fighters. There are also monuments from the Second World War – concentration camp Red Cross and Bubanj.