The triangle turret is part of the fortifying system of Serdica and it lays into the basement of a residential building, situated at the crossing of Exarch Joseph str. and Maria Louisa Blvd. It is dated back to the time of Emperor Justinian I (527-565 A.D.). The fortified wall of Serdica is thickened outside by entirely brick belt and provided with additional triangle turret. It is nothing like the remains found so far. It has the shape of an isosceles triangle, pointed with its sharp end to the north. In today's look the turret has a plinth made of stone blocks and construction entirely of brick on top. The two side exits ensure the possibility of sudden appearance of the defenders on the turret. They have thresholds of stone blocks.