enduring conflict between the Romans and the Parthians, and then,
after 224, between the Romans and the Sasanians, ensured a long-
lived demand for effective frontier allies. Competition for influence at
the fringes of imperial power provided opportunities for petty kings,
adventurers, and local rulers to form alliances with one, or both, of
the two empires. The list of potential allies was long; the Romans
formed agreements with kings of Armenia, with the Lazi and Tzani,
with groups of Avars, with Slavs, Huns, and, of course, when imperial
interests shifted southwards, with Arabs.
The conflict between Rome and Iran was not new. L. Cornelius
Sulla had concluded a treaty of friendship with the Parthians during
the last century of the Republic, but Roman ambitions brought
Crassus to defeat at Carrhae in 53
BC and began a long, drawn-out
conflict punctuated by periods of wary peace. Trajan pushed the
Roman frontiers into Armenia, Mesopotamia, and Arabia; his rule
was instrumental in establishing an enduring Roman interest in the
east.
80
At the end of the second century, Septimius Severus launched
an ambitious invasion of the Parthian Empire, capturing Ctesiphon
and occupying northern Mesopotamia. One of the consequences of
these actions was a greater commitment to the Near East, and a
greater frequency of conflict.
81
Much later, the conflict took a new
turn when the Parthians were overthrown by Ardashir, the first of the
including Roman classicising historians and ecclesiastical histories composed in
Greek and Syriac. For an overview, especially on the ideology of the Sasanians and
the efficiency of government, a driving force in the threat which they posed to the
Romans, see J. Howard-Johnston, ‘State and society in late antique Iran’,in
V. S. Curtis and S. Stewart (eds.), The Idea of Iran, iii: The Sasanian Era (London,
2008), 118–31. Generally, on Rome and Iran in the Near East: F. Millar, The Roman
Near East. 31
BC–AD 337 (Cambridge, Mass., 2001); R. C. Blockley, East Roman Foreign
Policy: Formation and Conduct from Diocletian to Anastasius (London, 1992); Isaac,
Limits; G. Greatrex, ‘Byzantium and the east in the sixth century’, in Maas (ed.),
Cambridge Companion to the Age of Justinian, 477–509; id., Rome and Persia at War,
502–532; J. Howard-Johnston, ‘The two great powers in Late Antiquity: a compar-
ison’, in Averil Cameron (ed.), The Byzantine and Early Islamic Near East, iii: States,
Resources and Armies (Princeton, 1995), 157–226; B. Dignas and E. Winter, Rome and
Persia in Late Antiquity: Neighbours and Rivals (Cambridge, 2007), esp. the concise
historical sketch pp. 9–49; A. D. Lee, Information and Frontiers: Roman Foreign
Relations in Late Antiquity (Cambridge, 1993), esp. 15–23.
80
Millar, Roman Near East, esp. 99–102, on Trajan, campaign of AD 114 in
Armenia; Mesopotamia, 115–16, and in Arabia, at the Persian Gulf, before his death
in 117, and Bowersock, Roman Arabia,81–5.
81
Isaac, Limits, 15; Millar, Roman Near East, 120–6.
30 Introduction