"Berthold was a younger son of Berthold I of Zähringen and initially supported Rudolf of Rheinfelden against King Henry IV. In 1077, both the Zähringer and Rheinfeldener were relieved of their titles and possessions by the king. Berthold I of Zähringen died in 1078 and his son Berthold inherited his claims, including a claim to the Duchy of Swabia. In 1079, Berthold married Agnes of Rheinfelden, Rudolf´s daughter.
In the following years, he became a strong supporter of Rudolf´s eldest son, Berthold of Rheinfelden, against the king. He was also at odds with Frederick of Büren and the Bishops of Basel and Strasbourg. However, when the region quieted down in the late 1080s, Berthold is found as a witness to an exchange of land involving the Bishop of Basel (1087)." - (en.wikipedia.org 01.11.2019)
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