"The identity of Berthold´s mother is disputed. She is sometimes said to be Rudolf´s first wife, Matilda of Germany (sister of Henry IV), and sometimes said to be Rudolf´s second wife, Adelaide of Savoy (if this were the case, then Berthold must have been born after c.1062), and sometimes said to be Rudolf´s son by another, unknown, wife.
After the death of his wife, Adelaide of Savoy, in 1079, Rudolf needed a new supervisor of the south German resistance, since he was himself confined to Saxony and cut off from his allies in Swabia. Rudolf therefore made his son, Berthold, Duke of Swabia. Henry, however, appointed Frederick of Büren, who had lands strategically located much to his advantage." - (en.wikipedia.org 01.11.2019)
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