In 1158 Frederick was back in Italy and held another great assembly at Roncaglia. He summoned hither certain teachers of the Roman law from Bologna (where the revived study of the law was actively pursued), as well as representatives of the towns, to decide exactly what his rights as emperor were. There was little danger but that those versed in a law which declared that "whatsoever the prince has willed has the force of law," should give the emperor his due. His _regalia_, or governmental prerogatives, were declared to consist in feudal suzerainty over the various duchies and counties, and in the right to appoint magistrates, collect tolls, impose an extraordinary war tax, coin money, and enjoy the revenue from fisheries and from salt and silver mines. Such persons or towns as could produce proof that any of these privileges had been formally conceded to them might continue to enjoy them; otherwise the emperor assumed them. As most of the towns had simply succeeded to the rights of the bishops and had no legal proofs of any concessions from the emperor, this decision meant the loss of their independence. The emperor greatly increased his revenue for the moment; but these extreme measures and the hated governors whom he appointed to represent him were bound to produce ultimate revolt. It became a matter of life and death to the towns to get rid of the imperial officials and taxgatherers. [Sidenote: The destruction of Crema and Milan.] The town of Crema refused to level its walls at the command of the emperor. It had to undergo a most terrible siege and finally succumbed. Its citizens were allowed to depart with nothing but their lives, and the place was given over to plunder and destruction. Then Milan drove the emperor's deputies from the gates. A long siege brought even this proud city to terms; and the emperor did not hesitate to order its destruction, in spite of its commercial and political importance (1162). It is a melancholy commentary upon the relations between the various towns that Milan's neighbors begged to be permitted to carry out her annihilation. Her inhabitants were allowed to settle in the neighborhood of the spot where their prosperous city had stood, and from the rapidity with which they were able to rebuild it later, we may conclude that the demolition was not so thoroughgoing as some of the accounts imply. [Sidenote: The Lombard towns secretly unite to form the Lombard League.]