*Wars with the Marcomanni, Quadi and Iazyges: 167–175 A. D.* In the meantime a dangerous situation had arisen on the Danubian frontier, where, probably in consequence of the pressure of migratory peoples, the Marcomanni, Quadi and the Sarmatian Iazyges united in an attempt to force their way into the Roman provinces. The army of the Danube had been weakened to reinforce the Syrian troops in the Parthian war and this enabled the barbarians to penetrate the frontier defences and ravage Noricum and Pannonia as far as Aquileia at the head of the Adriatic. The two Augusti proceeded to the scene of war, and after a protracted struggle in which Dacia suffered from a hostile invasion, the enemy were forced to make peace. The Marcomanni submitted in 172, and the Quadi and Sarmatians in 175 A. D. They were forced to surrender the prisoners carried off from the Roman provinces, over 160,000 in number, and to furnish military aid to Rome, while large numbers of them were settled on waste lands south of the Danube under the obligation of tilling the soil and rendering military service. The Roman victory was commemorated by the erection of a column at Rome with sculptures picturing incidents of the war, in imitation of Trajan’s memorial. In addition to the prosecution of this war, the strength of the empire had been taxed by serious outbreaks in Mauretania, Gaul and Egypt. *Revolt of Avidius Cassius, 175 A. D.* The complete subjugation of the northern foe was hindered by the revolt of Avidius Cassius, the general who had distinguished himself in the Parthian war and had suppressed the revolt in Egypt. Verus, the colleague of Aurelius, had died in 169, and at a rumor of the death of Aurelius himself in 175 A. D., Cassius proclaimed himself Imperator in Syria. Thereupon Aurelius hastened to conclude peace with the Sarmatians and proceeded to the East. Upon his arrival he found that Cassius had been killed by his own soldiers. Soon afterwards Commodus, the son of Aurelius, received the title Augustus and became co-ruler with his father (177 A. D.). *Second war with the Marcomanni and Quadi, 177–180 A. D.* In 177 A. D. war broke out anew with the Quadi and Marcomanni. Aurelius again took command on the Danube and after two years’ fighting had won so complete a victory that he contemplated the annexation of the region occupied by these peoples. But for a second time he was robbed of the fruits of his toil, on this occasion by the hand of death, 17 March, 180 A. D. The principate passed to his son and colleague, Commodus.