The removal of an effeminate tyrant made way for a succession of heroes. The indignation of the people imputed all their calamities to Gallienus, and the far greater part were, indeed, the consequence of his dissolute manners and careless administration. He was even destitute of a sense of honor, which so frequently supplies the absence of public virtue; and as long as he was permitted to enjoy the possession of Italy, a victory of the barbarians, the loss of a province, or the rebellion of a general, seldom disturbed the tranquil course of his pleasures. At length, a considerable army, stationed on the Upper Danube, invested with the Imperial purple their leader Aureolus; who, disdaining a confined and barren reign over the mountains of Rhætia, passed the Alps, occupied Milan, threatened Rome, and challenged Gallienus to dispute in the field the sovereignty of Italy. The emperor, provoked by the insult, and alarmed by the instant danger, suddenly exerted that latent vigor which sometimes broke through the indolence of his temper. Forcing himself from the luxury of the palace, he appeared in arms at the head of his legions, and advanced beyond the Po to encounter his competitor. The corrupted name of Pontirolo still preserves the memory of a bridge over the Adda, which, during the action, must have proved an object of the utmost importance to both armies. The Rhætian usurper, after receiving a total defeat and a dangerous wound, retired into Milan. The siege of that great city was immediately formed; the walls were battered with every engine in use among the ancients; and Aureolus, doubtful of his internal strength, and hopeless of foreign succors already anticipated the fatal consequences of unsuccessful rebellion.