The development of new, effective firearms at the end of the 14th century, especially artillery, with which medieval armies were armed, meant a sudden threat to the defences of castles, because their former builders did not know long-range firearms at the beginning of the 13th century. This modernisation of combat technology also proved fatal for Sternberg Castle in 1467, when King George of Poděbrady's troops besieged the residence of the rebellious Zdeněk Konopiště of Sternberg. The castle was then conquered, perhaps due to a lack of water and food, but above all by very effective artillery fire from the conquerors, directed from the south from a higher firing position, from where the castle was most vulnerable. It was therefore imperative to accommodate this point of threat in a broadly conceived defensive system, and the construction of an advanced bastion was the best way to do this. It was located on the strategically important highest point of a long, rocky ridge, cut off to the south by a wide, artificially dug ditch.
A massive central tower was created here, shaped into a sharp edge on the south side, designed to knock enemy projectiles to the sides. The space on the tower floor, accessible by a spiral staircase, shows an ingenious arrangement of gunports designed to fire light cannon. A square opening in the floor opens onto the high, dark ground floor, which served as a powder room and supply room for the tower crew. The present ground floor entrance was only breached in the 19th century. The area around the main tower is protected by a massive horseshoe-shaped perimeter wall with loopholes, only the torso of the front part of which remains.