The Chronometer (Astronomical Clock) has been erected to commemorate the victory in 1645 (in the Thirty Years’ War) when the city was under attack by the Swedish army led by General Torstenson who was considered to be immortal. According to the legend the only way to kill him would be with a glass ball at midnight in a magical ritual. At some point during the siege, the Swedish commanders decided that the Swedes would only give up if they hadn’t conquered the city before noon. The citizens of Brno then changed the time of the church bell noon ringing one hour – making it ring at 11 o’clock instead of noon. Therefore today a glass marble is released from the Astronomical Clock every day at 11 o'clock.