In 502, Sasanian shah Kavadh I opened a major war against the Byzantine Empire, ending a long period without large-scale fighting. Late antique sources link the outbreak to frontier tensions and finance, including Kavadh’s demand for funds and Byzantine refusal. The war set the pattern for the next century: raids, sieges, and bargaining over fortified borderlands.
In August 502, Sasanian forces took Theodosiopolis (modern Erzurum), a key Byzantine stronghold in Armenia. The fall showed how vulnerable the Byzantine frontier could be early in the war and encouraged further Sasanian operations. It also highlighted Armenia and the Caucasus as recurring pressure points in later conflicts.
From October 502 to January 503, Kavadh I besieged and captured Amida (modern Diyarbakır). The prolonged siege and violent sack emphasized that fortified cities, not just open battles, were central to this rivalry. The event also influenced later Byzantine investment in stronger frontier fortifications.
In 505, Emperor Anastasius I began building up Dara (also called Anastasiopolis) as a major fortress close to the Sasanian-held city of Nisibis. The project was a direct response to weaknesses exposed in the Anastasian War, giving Byzantium a stronger base for defense and counterattacks. Dara later became one of the most contested sites in Roman–Sasanian warfare.
In 532, Byzantium and Sasanian Iran signed the so-called Perpetual (or Eternal) Peace, ending the Iberian War that had centered on the Caucasus kingdom of Iberia (in present-day Georgia). The agreement brought a pause in fighting and showed how disputes in the Caucasus could pull both empires into wider war. The “perpetual” peace proved temporary, breaking down within a decade.
Between February and June 541, Khosrow I’s forces captured the fortress of Petra in Lazica on the Black Sea coast. Control of Petra mattered because it affected trade routes and military access around the Caucasus. The struggle for Lazica became a long, costly war that expanded the battlefield beyond Mesopotamia into the Caucasus region.
In 550–551, Byzantine forces under Bessas retook Petra from its Sasanian garrison after a difficult siege. The reversal showed how neither side could easily hold key fortresses in the rugged Lazica theater. It also pushed the conflict toward grinding attrition, with repeated sieges and shifting local alliances.
In 562, a peace treaty often called the Fifty-Year Peace (or Treaty of Dara) ended the long war over Lazica. Under its terms, the Sasanians agreed to evacuate Lazica, and Byzantium agreed to pay an annual subsidy, reflecting how diplomacy and payments were part of frontier strategy. The treaty reduced open warfare but did not remove the underlying rivalry.
In 572, Emperor Justin II ended the treaty arrangement and war resumed on a large scale. The renewed fighting (572–591) combined Mesopotamian sieges with Caucasus campaigning and pulled in Arab allies on both sides. This breakdown showed how fragile long truces were when border politics and client states stayed contested.
In 573, Khosrow I captured Dara after a multi-month siege, taking a fortress built specifically to balance Sasanian power at Nisibis. Dara’s fall was a major strategic and psychological blow, since it anchored Byzantine defense in northern Mesopotamia. The event also helped drive political instability in Constantinople as the war escalated.
In 591, after a Sasanian civil war, Byzantine Emperor Maurice helped Khosrow II regain the throne, culminating in the battle at Blarathon. The resulting settlement favored Byzantium, expanding its influence in parts of the Caucasus and Armenia. This moment temporarily rebalanced the rivalry but also tied Khosrow II’s legitimacy to Byzantine help—an important factor in later events.
In 602, Byzantine Emperor Maurice was murdered and replaced by Phocas, creating a crisis of legitimacy. Khosrow II used Maurice’s death as a justification to renew war, starting the massive conflict of 602–628. This war became the most destructive of the series, spreading far beyond the normal border zone.
Beginning in 603, Sasanian armies pushed into Byzantine Armenia and over several years gained control over much of the region. Armenia mattered strategically because it connected Mesopotamia to the Caucasus and Anatolia. The campaign helped open routes for deeper Sasanian advances into Byzantine territory during the early phase of the war.
In 614, Sasanian forces captured Jerusalem after a siege during their wider Levant campaign. Byzantine and later Christian accounts emphasize that important relics, including the True Cross, were carried off to Persia, making the conquest politically and religiously charged. The loss deepened Byzantine morale problems and raised the stakes of the war.
From 618 to 621, Sasanian general Shahrbaraz conquered Byzantine Egypt, including Alexandria, bringing a core Byzantine province under Persian occupation. Egypt’s grain and tax revenues were crucial to the Byzantine state, so its loss weakened Constantinople’s ability to finance war. The conquest marked the high point of Sasanian expansion in the conflict.
In June–July 626, the Sasanians coordinated with Avar and Slavic forces to attack Constantinople. The city held out, and Byzantine naval control prevented Persian troops from effectively joining the assault across the Bosporus. The failure was a turning point: it protected the Byzantine capital and helped set up Heraclius’s push into Persian territory.
On December 12, 627, Emperor Heraclius defeated a Sasanian army near Nineveh in what is often treated as the war’s decisive battlefield victory. The battle disrupted remaining Sasanian resistance and allowed Heraclius to threaten the Persian heartland. It directly contributed to political collapse around Khosrow II soon afterward.
In 628, the Byzantine and Sasanian governments agreed to peace: occupied territories were returned and captives released, effectively restoring the prewar border (status quo ante bellum). The settlement ended the 602–628 conflict and closed the last and largest round of the Sasanian–Byzantine wars. Both empires emerged badly weakened, shaping the political landscape of the Middle East immediately afterward.
In early January 628, Heraclius’s forces sacked Dastagird, a major royal residence of Khosrow II near Ctesiphon, adding pressure on an already strained Sasanian state. Within weeks, Khosrow II was overthrown by his son (Kavad II), and the new regime quickly sought peace. The rapid shift shows how military defeat, elite politics, and exhaustion combined to end the long war.
Sasanian–Byzantine Wars (502–628 CE)