The struggle resumed and intensified under Ardashir's successor Shapur I; he invaded Mesopotamia and captured Hatra, a buffer state which had recently shifted its loyalty but his forces were defeated at a battle near Resaena in 243; Carrhae and Nisibis were retaken by the Romans. Encouraged by this success, the emperor Gordian III advanced down the Euphrates but was defeated near Ctesiphon in the Battle of Misiche in 244. Gordian either died in the battle or was murdered by his own men; Philip became emperor, and paid 500,000 denarii to the Persians in a hastily negotiated a peace settlement.