[Sidenote: Renewed fortifying of the Danube-frontier.] After the murder of Gallienus (268), perhaps on the news of it, the barbarians, again led by the Heruli, but this time with united forces, undertook an assault on the imperial frontier, such as there had not been hitherto, with a powerful fleet, and probably at the same time by land from the Danube.[145] The fleet had much to suffer from storms in the Propontis; then it divided, and the Goths advanced partly against Thessaly and Greece, partly against Crete and Rhodes; the chief mass resorted to Macedonia and thence penetrated into the interior, beyond doubt in combination with the bands that had marched into Thrace. But the emperor Claudius, who marched up in person with a strong force, brought relief at length to the Thessalonians oft besieged but now reduced to extremity; he drove the Goths before him up the valley of the Axius (Vardar) and onward over the mountains to upper Moesia; after various conflicts, with changing fortune of war, he achieved here in the Morava valley near Naissus a brilliant victory, in which 50,000 of the enemy are said to have fallen. The Goths retired broken up, first in the direction towards Macedonia, then through Thrace to the Haemus, in order to put the Danube between themselves and the enemy. A quarrel in the Roman camp, this time between infantry and cavalry, had almost given them once more a respite; but, when it came to fighting, the cavalry could not bear to leave their comrades in the lurch, and so the united army was once more victorious. A severe pestilence, which raged in all the years of distress, but especially then in those regions, and above all in the armies, did great injury doubtless to the Romans--the emperor Claudius himself succumbed to it--but the great army of the Northmen was utterly extirpated, and the numerous captives were incorporated in the Roman armies or made serfs. The hydra of military revolutions, too, was in some measure subdued; Claudius, and after him Aurelian, were masters in the empire after another fashion than could be said of Gallienus. The renewal of the fleet, towards which a beginning had been made under Gallienus, would not be wanting. The Dacia of Trajan was, and remained, lost; Aurelian withdrew the posts still holding out there, and gave to the possessors dislodged or inclined for emigration new dwellings on the Moesian bank. But Thrace and Moesia, which for a time had belonged more to the Goths than to the Romans, returned under Roman rule, and at least the frontier of the Danube was once more fortified. [Sidenote: Character of the Gothic wars.]