Lords of Hradec had to build the Black Tower along with the Old Palace and castle's walls at the beginning of 13th century. Such towers were called "Berfgrieds". Their reason was partly defensive but they weren't built in the line of defensive walls like fortified towers but stood often apart from other castle's buildings, connected with them just with light wooden walkways. They had the function of watchtowers and were prepared for cases of fight within the castle - as the refuge towers for the last resistance. The local Bergfried's only entrance was originally in the height of 13 m. The later structural development connected the tower with the Old Palace.
The tower's measurement are interesting. The height and circuit are the same - 32 m (104,99 ft. or 35yd.). The diameter makes slightly more than 10 m. The only wall of the tower is approximately 4 m thick (13,12 ft. or 4,37 yd.) up to 20 m of its height.
The Black Tower was also used as the prison. There were also well known personalities of Czech history among the people imprisoned in the local tower - controversial preacher Martin Houska in January 1421 and Baron Zikmund of Vartenberg who was imprisoned for the betrayal of Czech King Albrech in 1438. Baron Zikmund died in the tower after few weeks. In 1784, the new entrance into tower was created in the ground floor and the tower was used as a prison for "insubordinate dependants". The last inhabitants of the tower were two Russian bears, which brought earl Jaromír Černín from his travels in 1848.