During the Roman-Persian Wars, the Kingdom of Araba was a buffer state between the Roman Empire and the Parthian Empire, and the dynasty was mostly under influence of the latter. Its capital city Hatra was strongly fortified, and managed to repulse sieges by Roman emperors Trajan (in 117 AD) and Septimius Severus (in 193 and 197 AD). During the reign of Sanatruq II, the kingdom expanded, and as the Parthian Empire was succeeded by the Sasanian Empire, Hatra shifted its loyalty and became a vassal kingdom of the Romans.