“Cat and mouse” behaviour is not only a popular expression: the disputes of the lords of castles of former years were also reflected in their building activity. So the “Mouse” Castle, known as Deuernburg, is ultimately a stronghold standing in opposition to “Cat” Castle, in the conflict of the counts of Katzenelnbogen with the Electorate of Trier. The Trier Archbishop Boemund II constructed “Mouse” in 1356 in St. Goarshausen-Wellmich - and it was from the beginning directed against Rheinsfel Castle which lay upstream and belonged to the said counts of Katzenelnbogen. The same counts did not stand the threat to their customs clearance in St. Goar through the new stronghold on the other side of the Rhine for long. They completed their castle Neu-Katzenelnbogen - later known as “Cat” Castle - as an unfriendly answer, even before 1371. The two bulwarks together count among the most well-known sights in the Rhine Valley. In contrast to the “Enemy Cat”, the “Mouse” offers an impression of mediaeval castle-building with its reconstructed core building from 1900.