and Dacian legions and a large number of auxiliaries, Severus defeated and killed Clodius Albinus, securing his full control over the empire. Emperor War against Parthia In early 197 Severus left Rome and sailed to the east. He embarked at Brundisium and probably landed at the port of Aegeae in Cilicia, travelling on to Syria by land. He immediately gathered his army and crossed the Euphrates. Abgar IX, titular King of Osroene but essentially only the ruler of Edessa since the annexation of his kingdom as a Roman province, handed over his children as hostages and assisted Severus' expedition by providing archers. King Khosrov I of Armenia also sent hostages, money and gifts. Severus travelled on to Nisibis, which his general Julius Laetus had prevented from falling into Parthian hands. Afterwards Severus returned to Syria to plan a more ambitious campaign. The following year he led another, more successful campaign against the Parthian Empire, reportedly in retaliation for the support it had given to Pescennius Niger. His legions sacked the Parthian royal city of Ctesiphon and he annexed the northern half of Mesopotamia to the empire; Severus took the title , following the example of Trajan. However, he was unable to capture the fortress of Hatra, even after two lengthy sieges—just like Trajan, who had tried nearly a century before. During his time in the east, though, Severus also expanded the Limes Arabicus, building new fortifications in the Arabian Desert from Basie to Dumatha. Relations with the Senate and People Severus' relations with the Senate were never good. He was unpopular with them from the outset, having seized power with the help of the military, and he returned the sentiment. Severus ordered the execution of a large number of Senators on charges of corruption or conspiracy against him and replaced them with his favourites. Although his actions turned Rome more into a military dictatorship, he was popular with the citizens of Rome, having stamped out the rampant corruption of Commodus' reign. When he returned from his victory over the Parthians, he erected the Arch of Septimius Severus in Rome. According to Cassius Dio, however, after 197 Severus fell heavily under the influence of his Praetorian prefect, Gaius Fulvius Plautianus, who came to have almost total control of the imperial administration. At the same time, a bloody power crisis erupted between Plautianus and Julia Domna, Severus' influential and powerful wife, which