The fresco on the Bollwerk Tower was added during its restoration in 1893. At the time, wall murals followed precise rules. The characters depicted were figures that everyone could recognise. Here, the artist Ferdinand Wagner depicted the burgomaster Ulrich de Dornach in 1395 who warned the city of the imminent attack by knight Martin Malterer and his troops. The painting was restored in 1977 by Bernard Latuner.
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