Vologases later proceeded towards Nusaybin and laid siege to it, but aborted it due to Roman reinforcements and failed to capture the city. Afterwards, Severus started marching toward Euphrates and to South and took Seleucia and Babylon without resistance, although the Romans contended heavily in late 198 during the fall of Ctesiphon. However, the Romans did not manage to hold the captured regions; they had to retreat due to lack of provisions. The Romans decided to take Hatra while returning, but failed and tried once more in spring 199 to conquer Hatra, and were forced to cede control of Syria with heavy casualties. It must have been that "highly disruptive period of Vologases V's reign" and the raid and destruction of Mesopotamia by Severus when Papak probably united most of Pars under his rule. Apparently a peace treaty was then formed between the two powers, though the ancient historians have had no mention of it. Until Vologases' death in 206 or 207 and also Severus's in 211, the Parthian-Roman relations were peaceful. After Vologases V's death, his son Vologases VI rose to the throne; but shortly afterward, his reign was challenged by his brother Artabanus IV. In about 213, Artabanus launched a rebellion against his brother Vologases and took the rule of a large part of the Parthian Empire; it can be deduced from the coins found in Hamadan that he ruled the Median land.