The fortification system, that had been built after the foundation of the Hussite fortress and improved by following generations, rightly became a boast of the town. At that time the complicated defence system was second to none in all Central and Western Europe.

Its uniqueness was based on the combination of two circular walls - the main one and the bailey. If an enemy succeeded in getting over the first wall, the lower bailey, he was trapped in the moat - an area 6-10 metres wide between the two circular walls. At that moment he became an easy target for the defenders and must have lost courage to continue the attack. Several towers and cannon bastions were incorporated in the town walls which gave the defenders an opportunity to shoot at the enemy from either cannons or smaller weapons. Probably the best-preserved part of the fortification system is the Zizka Bastion, sometimes also called The Big Bastion. It used to control the access from the north and from the valley of the River Tismenický. Later it was used for housing, and thanks to that it has not been destroyed like the rest of the fortification system. The most vulnerable points of the unassailable stronghold were the gates, especially the New Gate, the access from the east. That was why the gate was shielded with a special fortification structure called the barbican. All these then unusually modern features prove how advanced the Hussite military engineering was. Although most of the town walls were destroyed in the 19th century, their remaining parts belong among the most valuable sights in the town. They were proclaimed a national cultural monument and are protected by the state.