The corner northeastern round turret of the fortifying system of Serdica is situated on Iskar Str. and Serdica Str. This archeological monument includes parts of the Eastern wall and The Northern wall preserved at a considerable height. Very well seen are the periods of construction: the end of 3rd century - mixed brick and stone masonry; the end of 5th century - brick belt. In a good shape are found parts of a wall thick 6 m at some places and the staircases climbing up the turret and the side exit leading out of the city.