Editing Diocletian (section)

===War with Persia===
{{see also|Roman–Iranian relations|Roman–Persian Wars}}

====Invasion, counterinvasion====
[[File:Diocletian medallion.jpg|thumb|left|Medallion of Diocletian, AD&nbsp;294]]
In 294, [[Narseh]], a son of Shapur who had been passed over for the Sassanid succession, came to power in Persia.{{sfnm|1a1=Potter|1y=2005|1p=292|2a1=Williams|2y=1985|2p=69}} 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 (emperor)|Valerian]] (r. 253–260) following his failed invasion of the [[Sasanian Empire]].{{sfn|Williams|1985|pp=69–70}}

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.<ref>[[Ammianus Marcellinus]] 23.5.11</ref>{{sfnm|1a1=Barnes|1y=1981|1p=17|2a1=CAH|2p= 81|3a1=Potter|3y=2005|3p=292|4a1=Southern|4y=2001|4p=149}} 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]].{{sfnm|1a1=Eutropius|1loc=9.24–25|2a1=Barnes|2y=1981|2p=17|3a1=CAH|3p=81|4a1=Millar|4y=1993|4pp=177–178}}  Diocletian may or may not have been present at the battle,{{sfn|Potter|2005|p=652}} 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.<ref>[[Eutropius (historian)|Eutropius]] 9.24–25; [[Theophanes Confessor]], [https://archive.org/details/ByzantineAndNearEasternHistoryAD284813/page/n55/mode/1up AM 5793].</ref>{{sfnm|1a1=Barnes|1y=1981|1p=17|2a1=CAH|2p=81|3a1=Potter|3y=2005|3pp=292–293}}{{refn|It is possible that Galerius's position at the head of the caravan was merely the conventional organization of an imperial progression, designed to show a caesar's deference to his augustus, and not an attempt to humiliate him.{{sfn|Rees|2004|p=14}}|group="Note"}}

[[File:Arch-of-Galerius-1.jpg|thumb|Detail of [[Galerius]] attacking [[Narseh]] on the [[Arch and Tomb of Galerius#Arch of Galerius|Arch of Galerius]] at [[Thessaloniki]], [[Greece]], the city where Galerius carried out most of his administrative actions{{sfn|Rees|2004|p=14}}{{sfn|Southern|2001|p=151}}]]
Galerius was reinforced, probably in the spring of 298, by a new contingent collected from the empire's Danubian holdings.{{sfnm|1a1=Barnes|1y=1981|1p=18|2a1=CAH|2p=81|3a1=Millar|3y=1993|3p=178}} Narseh did not advance from Armenia and Mesopotamia, leaving Galerius to lead the offensive in 298 with an attack on northern Mesopotamia via Armenia.{{sfnm|1a1=Millar|1y=1993|1p=178|2a1=Potter|2y=2005|2p=293}}{{refn|[[Faustus of Byzantium]]'s history refers to a battle that took place after Galerius set up base at [[Satala]] (Sadak, Turkey) in [[Armenia Minor]], when Narseh advanced from his base at Oskha to attack him.{{sfn|CAH|p=81}}|group="Note"}} It is unclear if Diocletian was present to assist the campaign; he might have returned to Egypt or Syria.{{refn|Lactantius criticizes Diocletian for his absence from the front,{{sfn|Lactantius|loc=9.6}} but Southern, dating Diocletian's African campaigns one year earlier than Barnes, places Diocletian on Galerius's southern flank.{{sfn|Southern|2001|pp=151, 335–336}}|group="Note"}} Narseh retreated to Armenia to fight Galerius's force, putting himself at a 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 [[Battle of Satala (298)|second encounter]], Roman forces seized Narseh's camp, his treasury, his harem, and his wife.{{sfnm|1a1=Barnes|1y=1981|1p=18|2a1=Potter|2y=2005|2p=293}} Galerius continued down the Tigris, and took the Persian capital Ctesiphon before returning to Roman territory along the Euphrates.{{sfnm|1a1=Barnes|1y=1981|1p=18|2a1=Millar|2y=1993|2p=178}}

====Peace negotiations====
Narseh sent an ambassador to Galerius to plead for the return of his wives and children in the course of the war, but Galerius dismissed him.{{sfn|Barnes|1981|p=18}} Serious peace negotiations began in the spring of 299. The ''magister memoriae'' (secretary) of Diocletian and Galerius, Sicorius Probus, was sent to Narseh to present terms.{{sfn|Barnes|1981|p=18}} The conditions of the resulting [[Peace of Nisibis (299)|Peace of Nisibis]] were heavy:{{sfn|Potter|2005|p=293}}  Armenia returned to Roman domination, with the fort of Ziatha as its border; [[Kingdom of Iberia (antiquity)|Caucasian Iberia]] would pay allegiance to Rome under a Roman appointee; Nisibis, now under Roman rule, would become the sole conduit for trade between Persia and Rome; and Rome would exercise control over the five satrapies between the Tigris and Armenia: [[Angeghtun|Ingilene]], Sophanene ([[Sophene]]), Arzanene ([[Aghdznik]]), [[Corduene]] (Carduene), and Zabdicene (near modern [[Hakkâri (city)|Hakkâri]], Turkey). These regions included the passage of the Tigris through the [[Anti-Taurus Mountains|Anti-Taurus]] range; the [[Bitlis]] pass, the quickest southerly route into Persian Armenia; and access to the [[Tur Abdin]] plateau.{{sfnm|1a1=Millar|1y=1993|1pp=178–179|2a1=Potter|2y=2005|2p=293}}

A stretch of land containing the later strategic strongholds of Amida ([[Diyarbakır]], Turkey) and [[Bezabde]] came under firm Roman military occupation.{{sfn|Millar|1993|p=178}} With these territories, Rome would have an advance station north of Ctesiphon, and would be able to slow any future advance of Persian forces through the region.{{sfn|Potter|2005|p=293}}  Many cities east of the Tigris came under Roman control, including [[Tigranocerta|Tigranokert]], [[Siirt|Saird]], [[Silvan, Diyarbakır|Martyropolis]], [[Bitlis|Balalesa]], [[Bakhchisaray|Moxos]], [[Duhok, Iraq|Daudia]], and Arzan&nbsp;– though under what status is unclear.{{sfn|Millar|1993|p=178}} At the conclusion of the peace, Tiridates regained both his throne and the entirety of his ancestral claim.{{sfn|Barnes|1981|p=18}} Rome secured a wide zone of cultural influence, which led to a wide diffusion of [[Syriac Christianity]] from a center at Nisibis in later decades, and the eventual Christianization of Armenia.{{sfn|Potter|2005|p=293}} 

To strengthen the defence of the east Diocletian had a fortified road constructed at the southern border, where the empire bordered the Arabs, in the year 300. This road would remain in use for centuries but proved ineffective in defending the border as conventional armies could not operate in the region.<ref name="RR">{{Cite book|title=Rome Resurgent: War and Empire in the Age of Justinian|last=Heather, P. J. (Peter J.)|isbn=978-0-19-936274-5|location=New York |publisher=Oxford University Press |oclc=1007044617|year = 2018}}</ref>