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The “Long Peace” (CE 387–502)

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Summary

The period is often described by historians as one of the longest sustained intervals of peace between the Roman and Sasanian empires. It began with the settlement negotiated between Emperor Theodosius I and the Sasanian king Shapur III in the 380s—usually dated to 387, though some scholars argue for 384 or 389—and lasted until the outbreak of the Anastasian War in 502. For more than a century, Roman-Persian disputes were settled by negotiation rather than hostilities and the frontier was remarkably stable by the standards of Late Antiquity.  

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After decades of conflict over Armenia, Shapur III and Theodosius I reached a diplomatic settlement known as the Peace of Acilisene or the Partition of Armenia. Armenia, long the principal cause of Roman-Persian wars, was divided into Roman and Persian spheres of influence. Rome retained the western districts, while the Sasanians gained the larger eastern portion. Rome also effectively recognized Sasanian predominance in Iberia (eastern Georgia).  

The importance of the agreement was not simply territorial. It removed the principal source of strategic friction between the two superpowers. Both empires faced pressing problems elsewhere:

  • The Romans confronted Gothic, Hunnic, and later Germanic pressures along the Danube and Rhine.
  • The Sasanians faced nomadic threats from Central Asia and political challenges on their eastern frontiers.  

Because each empire had stronger reasons to conserve resources than to fight the other, diplomacy became the preferred instrument of policy. The frontier in Mesopotamia remained largely unchanged, and both states cooperated in defending the Caucasian passes against northern nomadic incursions. Roman payments to Persia for frontier defense—viewed by the Romans as subsidies and by the Sasanians as tribute—became a recurring feature of relations.  

The fifth century consequently became a period of unusual stability:

  • Yazdegerd I (399–420) maintained generally cordial relations with the Eastern Roman Empire.
  • Theodosius II and successive Sasanian rulers frequently settled disputes through negotiation rather than war.
  • Commercial exchange flourished across Mesopotamia and the Silk Road corridors.
  • Christian and Zoroastrian communities continued to interact across imperial borders despite occasional religious tensions.

The peace was not absolute. There were diplomatic crises, frontier incidents, and a brief war in 421–422 under Bahram V and Theodosius II. Yet even that conflict ended quickly and restored the status quo. Historians therefore often treat the fifth century as an era of strategic equilibrium rather than uninterrupted tranquility.  

The settlement finally unraveled at the beginning of the sixth century. Internal difficulties in the Sasanian Empire under Kavadh I, disputes over frontier subsidies, and changing strategic circumstances led to the Anastasian War (502–506), ending more than a century of relative peace.  

Why the Long Peace Matters

The Roman-Sasanian détente of the fifth century was one of the most successful diplomatic arrangements of Late Antiquity. It:

  1. Stabilized the Near East for over a century.
  2. Allowed both empires to focus on other threats.
  3. Encouraged economic and cultural exchange across the frontier.
  4. Established diplomatic mechanisms that later rulers, including Justinian and Khosrow I, would inherit.  

Many historians see this period as a precursor to the sophisticated balance-of-power diplomacy that characterized later Roman-Persian relations.

Primary Sources

  • Faustus of Byzantium, History of the Armenians (Book VI).
  • Socrates Scholasticus, Ecclesiastical History.
  • Sozomen, Ecclesiastical History.
  • Theodoret, Ecclesiastical History.

Modern Scholarship

  1. Nina Garsoïan, The Armenian People from Ancient to Modern Times, Vol. I.
  2. Touraj Daryaee, Sasanian Persia: The Rise and Fall of an Empire.
  3. Geoffrey Greatrex and Samuel N.C. Lieu, The Roman Eastern Frontier and the Persian Wars, Part II (363–630 AD).
  4. James Howard-Johnston, East Rome, Sasanian Persia and the End of Antiquity.
  5. R.C. Blockley, “The Division of Armenia between the Romans and the Persians at the End of the Fourth Century A.D.” (Historia, 1987).  
  6. Cyril Toumanoff, Studies in Christian Caucasian History.
  7. Stephen H. Rapp Jr., The Sasanian World through Georgian Eyes.

Among modern works, Howard-Johnston, Greatrex & Lieu, and Daryaee are probably the best starting points for understanding why the Roman-Sasanian frontier remained so stable between the settlement of Shapur III and the wars of the early sixth century.

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