Complex sentence: He followed Valerian during his ultimately catastrophic campaign against the Persians in 259 or 260; however, he remained at Samosata during the fatal battle of Edessa and his role in the events before and after the battle is questionable.
Split into simpler sentences: He followed Valerian during his ultimately catastrophic campaign against the Persians in 259 or 260. However, he remained at Samosata during the fatal battle of Edessa and his role in the events before and after the battle is questionable.