Plaque depicting the Siege of Groningen by M. van Keulen, silver, 17th century. This plaque depicts the siege and relief of Groningen. The bishops of Cologne and Münster laid siege to the city from 9 July to 17 August 1672. Led by Karel von Rabenhaupt the city managed to overcome its attackers. After the bombardment of Groningen Bernhard van Galen, the bishop van Münster, became known as Bomber Berend.