Two thousand feet above the sea, on the very summit of one of the northern outliers of the rugged Swabian Alp that separates the valley of the upper Neckar from that of the upper Danube, stood the castle of Hohenstaufen, that gave its name to the most gifted house that ever ruled over the mediæval Empire. The hereditary land of the family lay around, and a few miles east, nearer the Neckar valley, lies the village of Weiblingen from which came the even more famous name of Ghibelline. The lords of this upland region were true Swabian magnates, who were gradually brought into greatness by their energy and zeal in supporting the Empire. In the darkest days of his struggle with the Church, Henry IV. had no more active or loyal partisan than Frederick of Büren or Hohenstaufen, whom he married to his daughter Agnes, and upon whom he conferred the duchy of Swabia. It was after the ancient fashion that the new Duke of Swabia should find his chief enemy in the Duke of Bavaria. But besides many a bitter feud with the papalist house of Welf or Guelf, Frederick had to deal with no less formidable enemies within his own duchy. The same disintegrating influences that were affecting all Germany were at work in Swabia. Berthold of Zähringen, a mighty man in the upper Rhineland, sought to attain the Swabian duchy by zealous championship of the papal cause. After long fighting with the Staufer, the lord of Zähringen was able to effect a practical division of the duchy. In 1097 he was allowed all ducal rights in those Swabian lands between Rhine and Alps, which in a later age became the centre of the Swiss confederation. He did not lose even the title of duke, so that with the Dukes of Zähringen as effective rulers of Upper Swabia, the Hohenstaufen influence was limited to the north. The first Hohenstaufen Duke of Swabia had, by the Emperor’s daughter, two sons, whose names were Frederick and Conrad. [Sidenote: Frederick and Conrad.] These nephews of Henry V. were always marked out by their uncle as his successors. They inherited as a matter of course the private possessions of the Salian house. They had already given proof that they were worthy of a high destiny. Frederick, the elder, succeeded to his father’s duchy of Lower Swabia. He was now thirty-five years old, strong, courageous, ambitious, and well conducted. He had further strengthened his position by marrying Judith, daughter of Henry the Black, the Guelfic Duke of Bavaria (died 1126), a match which seemed likely to bridge over the natural antagonism of the two great southern ‘nations’ of Germany. Conrad, the younger brother, had obtained from his uncle the duchy of Franconia. All south Germany might well seem united in support of Frederick’s succession to the Empire. But the hierarchical party feared lest the traditional attitude of the Staufer might imperil the triumph of the Church. The feudal nobles were alarmed lest too vigorous a ruler might limit their independence.