*Defeat of Niger and Albinus.* But the position of Severus was not yet secure, for Niger had been recognized in the eastern provinces and also had a strong following in Rome. He was preparing to march upon Italy and had already occupied Byzantium. Severus at once set out to anticipate his attack. After investing Byzantium he crossed over to Asia Minor and defeated the forces of his rival near Cyzicus and Nicaea, forcing them to withdraw south of the Taurus mountains. The Cilician Gates were forced and Niger decisively beaten in a battle at Issus (194 A. D.). He tried to escape into Parthia but was overtaken and killed. Severus advanced across the Euphrates to punish the Parthian king for his support of Niger. He occupied northern Mesopotamia, and made Nisibis a Roman colony and frontier fortress (196 A. D.). In the same year Byzantium was taken, its fortifications destroyed, and its inhabitants deprived of the right of municipal organization. Severus had brought his Parthian campaign to a hasty conclusion, for in the West Clodius Albinus, feeling his position insecure, had assumed the title of Augustus and occupied Gaul. Severus now elevated his eldest son Bassianus, better known as Caracalla, to the position of Caesar with the additional title of _imperator designatus_, and set out to meet the usurper. In a great battle at Lugdunum, in which 150,000 men are said to have fought on either side, the army of Severus was victorious and Albinus fell by his own hand (197 A. D.). Many of his adherents, including numerous senators, were put to death. V. THE DYNASTY OF THE SEVERI, 197–235 A. D. *The Parthian war of 197–199 A. D.* Severus was now unchallenged ruler of the empire. Shortly after the defeat of Albinus, he returned to the East and resumed hostilities against the Parthians, whose king, Vologases IV, had taken advantage of his absence to invade Armenia and Mesopotamia and was besieging Nisibis. Severus relieved the beleaguered town and pressed on into the enemy’s territory, where he sacked the two Parthian capitals, Seleucia and Ctesiphon, in 198 A. D. By a peace arranged in the next year northern Mesopotamia was ceded to Rome and was organized as a province under a governor of equestrian rank.