The Siege of Tomis Ends: Plague Forces Avar Retreat (598)
On March 30, 598, the Avar khagan Bayan I lifted his siege of the Roman fortress-city of Tomis on the Black Sea coast and withdrew his forces north of the Danube River. The retreat came after an outbreak of plague tore through his combined Avaro-Slavic army, crippling its ability to continue the campaign. The episode marked a significant, if temporary, reprieve for Emperor Maurice's beleaguered Balkan provinces during decades of conflict with the Avars and their Slavic allies.
The Avar Threat to the Danubian Frontier
By the late 590s, the Avars had emerged as the dominant power on the Roman Empire's northern frontier, having subjugated numerous Slavic tribes and forged a formidable confederation capable of fielding large armies. Under their khagan Bayan I, the Avars repeatedly crossed the Danube to raid and besiege Roman cities in Moesia and Scythia Minor, exploiting the empire's preoccupation with its long war against Sassanid Persia. Tomis, a well-fortified port city on the western Black Sea coast in modern-day Constanța, Romania, represented a strategic prize: its capture would have given the Avars a foothold deep within Roman territory and disrupted vital communication and supply lines along the coast. Roman defenses in the region had been stretched thin for years, as successive emperors struggled to spare troops for the Balkans while Persian campaigns demanded attention in the east. Bayan's siege of Tomis in early 598 thus represented one of the most serious Avar threats to Roman control of the lower Danube frontier, testing whether the empire could hold its northern provinces even as it sought to stabilize its eastern one.
Did You Know?
According to some contemporary accounts, the plague that struck Bayan I's army near Tomis in 598 was so severe that it killed several of the Avar khagan's own sons, a personal loss that likely contributed to his decision to abandon the siege entirely.
Plague Breaks the Siege
The siege of Tomis did not end through Roman military victory but through a catastrophic outbreak of plague within the besieging Avaro-Slavic army. Disease had periodically ravaged populations across the Mediterranean and Near East since the devastating outbreak of the Plague of Justinian in 541–542, and recurring waves continued to strike both Roman and barbarian populations throughout the sixth century. Contemporary sources indicate that the epidemic struck Bayan's forces with severe mortality, decimating his troops and, according to some accounts, even claiming the lives of several of his own sons. The loss of manpower and morale left the Avar army in no condition to sustain a prolonged siege operation against a fortified Roman stronghold. Facing the collapse of his campaign from within rather than from Roman resistance, Bayan had little choice but to abandon the operation. On March 30, 598, he ordered his forces to withdraw from Tomis and retreat northward across the Danube back into Avar-controlled territory, ending the immediate threat to the city and providing Emperor Maurice's administration with a crucial, if fortuitous, respite from Avar pressure on this stretch of the frontier.
Aftermath and Broader Significance
The plague-driven retreat from Tomis fit within the larger pattern of Maurice's Balkan campaigns, which had grown increasingly successful after 591 when a favorable peace with Persia allowed the emperor to redirect experienced veteran troops to the northern frontier. Maurice, alongside Anastasius I, stood out among late antique emperors for his sustained commitment to defending the Balkans rather than treating the region as a secondary theater. Roman commanders such as Priscus and Peter achieved a series of victories against the Avars and Slavs in the years following 591, pushing back against incursions that had plagued the empire for decades. The events at Tomis in 598 demonstrated how disease, rather than battlefield tactics alone, could shape the outcome of ancient and medieval warfare, weakening even powerful confederations like the Avars at critical moments. However, the reprieve proved temporary: Maurice's overthrow and execution in 602 during a military mutiny led by Phocas soon unraveled many of his hard-won Balkan gains, and the Avars and Slavs would resume their pressure on the frontier, eventually overwhelming Roman defenses in the region during the following decades.