Diocletian
Invasion, counterinvasion

In 294, Narseh, a son of Shapur who had been passed over for the Sassanid succession, came to power in Persia. In early 294, Narseh sent Diocletian the customary package of gifts between the empires, and Diocletian responded with an exchange of ambassadors. Within Persia, Narseh was destroying every trace of his immediate predecessors from public monuments. He sought to identify himself with the warlike kings Ardashir I (r. 226–241) and Shapur I (r. 241–272), who had defeated and imprisoned Emperor Valerian (r. 253–260) following his failed invasion of the Sasanian Empire.

Narseh declared war on Rome in 295 or 296. He appears to have first invaded western Armenia, where he seized the lands delivered to Tiridates in the peace of 287. He moved south into Roman Mesopotamia in 297, where he inflicted a severe defeat on Galerius in the region between Carrhae (Harran, Turkey) and Callinicum (Raqqa, Syria), suggested by the historian Fergus Millar to have been somewhere on the Balikh River. Diocletian may or may not have been present at the battle, but he quickly divested himself of all responsibility. In a public ceremony at Antioch, the official version of events was clear: Galerius was responsible for the defeat; Diocletian was not. Diocletian publicly humiliated Galerius, forcing him to walk for a mile at the head of the Imperial caravan, still clad in the purple robes of the Emperor.

Galerius was reinforced, probably in the spring of 298, by a new contingent collected from the empire's Danubian holdings. Narseh did not advance from Armenia and Mesopotamia, leaving Galerius to lead the offensive in 298 with an attack on northern Mesopotamia via Armenia. It is unclear if Diocletian was present to assist the campaign; he might have returned to Egypt or Syria. Narseh retreated to Armenia to fight Galerius's force, to Narseh's disadvantage; the rugged Armenian terrain was favorable to Roman infantry, but not to Sassanid cavalry. In two battles, Galerius won major victories over Narseh. During the second encounter, Roman forces seized Narseh's camp, his treasury, his harem, and his wife. Galerius continued down the Tigris, and took the Persian capital Ctesiphon before returning to Roman territory along the Euphrates.
combination:two_responses