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The Roman-Parthian War of 161-166, also known as the Parthian War of Lucius Verus, was a conflict between the Roman Empire and the Parthian Empire. The war began when the Parthians invaded Armenia, which was a Roman client state. Pertinax, who would later become Roman emperor, served as a military tribune in the Roman army during this war. He distinguished himself in battle, earning praise from his superiors.