After he conceded the Duchy of Swabia to the Staufer in 1098, the title of "Duke of Zähringen" was created for him, in use from c. 1100 and continued by his successors until 1218.
In the following years, he became a strong supporter of Rudolf's eldest son, Berthold of Rheinfelden, against the king.
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).
At first only valid in Swabia, it was soon extended to Bavaria and strengthened the opposition to the emperor in southern Germany.
Berthold, beginning in 1090, extended his power into the Breisgau so that the Zähringer territory extracted itself from the influence of the Swabian duke.
With the displacement of the counts of Hohenburg from the region of the Black Forest, Berthold successfully turned it into his centre of power.