Henry’s relations with Frederick had long been strained. In 1232 he visited his father in Friuli, and was forced to renew his oaths of obedience. But his blunders and follies crowned all his enterprises with failure, and, after his father had been forced to disavow all responsibility for his rash deeds, the young king strove to unite the towns and the lesser nobles in revolt against the Emperor (1234). [Sidenote: Revolt and Ruin of Henry, 1335.] In 1235 Frederick was compelled to appear in Germany, where he easily put down his son’s rebellion. The cities adhered for the most part to the Emperor, and the ‘ministeriales’ and lesser nobles were not strong enough to stand alone. On the advice of the peace-loving Hermann of Salza, the young king made his submission to his father. His punishment was perpetual imprisonment in Apulia. In 1242, wearied with the restraint, he rode his horse over a precipice, and perished. [Sidenote: The Diet of Mainz and the English marriage, 1235.] Never was Frederick’s power so strongly manifested as during his visit to Germany in 1235. In the summer he celebrated at Worms his third marriage, with Isabella of England, the sister of Henry III., and soon afterwards held a numerously attended Diet at Mainz, where he published a series of famous constitutions, in some of which he sought to extend to Germany some of the principles that had for so long inspired his Sicilian policy. He established a court justiciar [_justiciarius curiæ_], who was to hold sessions of his court on all lawful days, hearing all causes save the high matters which the Emperor reserved for himself. This class included all the questions of dispute that might arise between the great vassals. Frederick strove to limit private war to cases where justice should be denied, and to raise up beside the courts of the princes the imperial court which he had thus reorganised. But at the same time he renewed the former privileges granted to the princes, and thus made his reforms of no effect. The feudal magnates were still to exercise every regalian right, the bishops were still to keep a tight hold over their see towns, and the free municipalities were still to renounce the protection of their ‘Pfahlbürger,’ and see their independence circumscribed by the local grandees. The lesser nobility soon succumbed before these blows, and the future of Germany was thus intrusted to the great feudatories. A good illustration of this is the circumstance that the ancient power of electing the kings passed away from the general assembly of the barons to the limited circle of magnates, who were later known as the seven electors. In the same conciliatory spirit, those who had a hand in the revolt of King Henry were fully pardoned, and special concessions to the more powerful princes bound them individually to the imperial cause. Among these may be specially mentioned the recognition of Otto of Lüneburg, the heir of