 His legions sacked the Parthian royal city of Ctesiphon and he annexed the northern half of Mesopotamia to the empire, taking 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, he also expanded the "Limes Arabicus", building new fortifications in the Arabian Desert from Basie to Dumatha.