Original: In 163, while Statius Priscus was occupied in Armenia, the Parthians intervened in Osroene, a Roman client in upper Mesopotamia, just east of Syria, with its capital at Edessa.
Simplified: In 163, while Statius Priscus was occupied in Armenia, the Parthians intervened in Osroene, a Roman client state in upper Mesopotamia, just east of Syria, with its capital at Edessa.