Berthold was a younger son of
Berthold I of Zähringen, and he 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 Stauf 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). Tensions rose again in 1090, when Berthold of Rheinfelden died. At that point, Berthold of Zähringen asserted his claims to the Rheinfeldener inheritance in
Burgundy, but not their titles, which went to Berthold of Rheinfelden's younger brother, Otto von Wetter(au)-Rheinfelden. He also placed a claim on the Duchy of Swabia. Supported by the
Welfs and the
Papacy, he was elected duke in opposition to Frederick in 1092. In that same year, he was chosen as
Duke of Carinthia and
Margrave of Verona (like his father) by those who opposed
Duke Henry V. Berthold, also like his father, never held any real power in Carinthia. In 1093, Berthold and
Welf IV signed a "peace oath" at
Ulm. At first only valid in Swabia, it was soon extended to Bavaria and strengthened the opposition to the emperor in southern Germany. Around 1098, Berthold and Frederick came to terms, whereby Frederick kept Swabia, but Berthold was given the
Reichsvogtei (or imperial estates, depending on the source) of
Zürich and allowed to keep a ducal title. By this step, the relationship between the Zähringer and Henry IV improved. In 1105, Berthold was the closest ally of Henry's son,
Henry V, who rebelled against his father. Beginning in 1090, Berthold extended his power into the
Breisgau so that the Zähringer territory extracted itself from the influence of the Swabian duke. In 1091, he abandoned
Zähringen Castle as his main residence in favour of the newly built
Freiburg Castle. Berthold was the first of the Zähringer to hold the title of "Duke of Zähringen" (from around 1100). He established his rule with the foundation of monasteries and other settlements in the
Black Forest. His territory was small, and he had little opportunity for expansion. His ducal title was described by
Otto of Freising as one of the first "empty titles" in medieval Germany – a title signifying little in the way of governmental or territorial significance. His was not a political or military office, nor a tribal or territorial command. Rather, his ducal title was a mere dignity, and his estates were family possessions. In 1093, he founded the
Benedictine monastery of Saint Peter, which became the family mausoleum. The monasteries that he founded were usually reformed monasteries, which were hostile to the emperor. With the displacement of the
counts of Hohenburg from the region of the Black Forest, Berthold successfully turned it into his centre of power. By the end of his life, Berthold's estates amounted to a justification of his grandiose title. He was succeeded as Duke of Zähringen in 1111 by his son
Berthold III. His youngest son,
Conrad, succeeded Berthold III in 1122. Among his other children, his daughter Agnes married
William II (the German), Count of Burgundy(1085–1125). ==References==