Serdika Ancient Fortress, Sofia City
The ruins of an antique fortress called Serdika are situated in the subway between the Presidency and Council of ministers in center of Sofia. The town of Serdika is founded in the II c. BC by the Thracian tribe Serds. Serdika used to be the favourite town of the Roman emperor Konstantin The Great. Serdika was surrouded by a wall with four gates and watchtowers pointing to the four directions of the world.