Byzantine Fronts and Strategies 300-1204 259

Chapter 8 Byzantine Fronts and Strategies 300-1204

Denis Sullivan

1 Period of Transition 300-502: Rome to Byzantium*

The period 293 to 502, from Diocletian to Anastasios, marked a new approach to sharing imperial administrative and defensive responsibilities in the late Roman Empire. Diocletian’s (r. 284-305) tetrarchic collegial system saw two Augusti and two Caesars with headquarters not in Rome, but at Nikomedia, Sirmium, Milan and Trier, closer to the frontiers. He also separated provincial civil and military responsibilities, creating dukes to command specifically military forces along the land frontiers.1 The development of mobile field armies is generally seen as incipient with Diocletian, but more fully implemented and substantial under Constantine I.2 Constantine (r. 306-337) after 324 in effect created regional prefectures3 and although ruling as sole Augustus himself, he named his three sons and a nephew as Caesars.4 Permutations of the collegial system were attempted through much of the 4th century and into the fifth, but power sharing proved an “insoluble dilemma”.5 Valens, for example, made a disastrous decision to engage at Adrianople before reinforcements arrived from the West lest he share the glory of the victory with his counterpart Gratian.6 In the 5th century the East, despite the demands of the Persian and Danube fronts, provided military assistance to the West in 410 (against Alaric), in 425 to aid Valentinian II, in the 430s against Gaiseric in North Africa, and in 440/1 for the joint expedition to Africa.7

* This paper was submitted in September 2014. Unfortunately, it has not been possible to con- sider related research published since that time. I am grateful to Professors Muriel Atkin and Elizabeth Fisher of The George Washington University for numerous valuable suggestions during the preparation of this chapter. 1 Treadgold, Byzantium and its Army, pp. 8-9. 2 Nicasie, Twilight of Empire, pp. 40-41. See, however, Poulter, “The Lower Danubian Frontier in Late Antiquity”, p. 16. 3 Kelly, “Bureaucracy and Government”, p. 186. 4 Treadgold, History, p. 49. 5 Heather, Fall of the Roman Empire, pp. 130-31. 6 Ibid., p. 178. 7 Ibid., pp. 388-89.

Edward Luttwak8 has suggested that from the mid-3rd century and par- ticularly under Diocletian and Constantine Rome developed a “defence-in- depth” strategy (following earlier periods of “expansionist” and “preclusive” approaches), with forces and installations in reserve some distance behind the border to deal with incursions. His tripartite schematization and even the possibility of a Roman grand strategy have been criticized from a number of perspectives and remain contentious. Everett Wheeler, however, while not endorsing Luttwak’s specific formulation, analysed the debate and argued per- suasively that the Romans were capable of planning and carrying out a “grand” strategy.9 More recently Peter Heather has argued contra Luttwak that frontier “policy” was guided more by political and propaganda needs of emperors than by sustained rational planning.10 The approach here (and below in the more specifically Byzantine material) will be to focus, however, not on the issue of grand strategy, but rather the application of the various components of strategy to the specific fronts in question. Diocletian appears to have constructed significant fortifications to counter Persian inroads into Syria, among them at Circesium on the Euphrates,11 and against Saracens with the Strata Diocletiana from Sura to southern Syria; he also built arms factories in Damascus.12 The Battle of Satala (298) in Armenia and subsequent Roman victories under the Caesar Galerius over the Persian king Narses led to the Treaty of Nisibis (299), which gave Rome authority over Armenia, Georgian Iberia and portions of northern Mesopotamia.13 The terms dictated by Diocletian and Galerius were conveyed to the Persian king by the magister memoriae Sicorius Probus.14 The treaty of 299 led to a relative peace on the front until 337 when the Persian king Shapur II invaded Roman Armenia. Constantine I responded with war preparations, including fortification projects at Amida; he rebuffed Persian diplomatic efforts to find a peaceful accommodation, but died at the begin- ning of the campaign.15 His son Constantius II conducted annual campaigns against Shapur over the next twelve years with some successes.16 In 359 Shapur renewed his attacks, besieging Amida in 359 and taking Singara in 360.

8 Luttwak, The Grand Strategy of the Roman Empire. 9 Wheeler, “Methodological Limits and the Mirage of Roman Strategy”, pp. 7-41 and 215-40. 10 Heather, “Holding the Line, pp. 227-46. 11 Millar, The Roman Near East, pp. 180-81. 12 Parker, The Roman Frontier in Central Jordan, vol. 2: p. 542. 13 See Blockley, “The Romano-Persian Peace Treaties”. 14 For an account of his embassy see Dodgeon/Lieu, The Roman Eastern, p. 116. 15 Fowden, “Constantine and the People of the Eastern Frontier”, spec. 392. 16 Treadgold, History, pp. 53 and 55.