Maurice's Balkan campaigns were a series of military expeditions conducted by Roman Emperor Maurice (reigned 582–602) in an attempt to defend the Balkan provinces of the Roman Empire from the Avars and the South Slavs. Maurice was the only East Roman emperor, other than Anastasius I, who did his best to implement determined Balkan policies during Late Antiquity by paying adequate attention to the safety of the northern frontier against barbarian incursions. During the second half of his reign, the Balkan campaigns were the main focus of Maurice's foreign policies, as a favourable peace treaty with the Persian Empire in 591 enabled him to shift his experienced troops from the Persian front to the region. The refocusing of Roman efforts soon paid off: the frequent Roman failures before 591 were succeeded by a string of successes afterwards.
Although it is widely believed that his campaigns were only a token measure and that Roman rule over the Balkans collapsed immediately after his overthrow in 602, Maurice was actually well on his way to forestalling the Slavic landfall on the Balkans and nearly preserved the order of Late Antiquity there. His success was undone only over ten years after his overthrow.
Retrospectively, the campaigns were the last in the series of classical Roman campaigns against the Barbarians on the Rhine and Danube, effectively delaying Slavic landfall on the Balkans by two decades. With respect to the Slavs, the campaigns had the typical trait of Roman campaigns against unorganized tribes and of what is now called asymmetric warfare.
Balkan Peninsula before 582
At Maurice's accession, the greatest omissions of his predecessors were to be found in the Balkans. Justinian I had neglected Balkan defences against the Slavs, who had threatened the frontier since 500 and pillaged the Balkan provinces ever since. Although he rebuilt the fortifications of the Danube Limes, he avoided campaigns against the Slavs, in favour of a policy focusing on the eastern and western theatres. His nephew and successor, Justin II, played off the Avars against the Gepids and later against the Slavs, but that only allowed the Avar Khaganate to become a more powerful threat than the Gepids and Slavs. As Justin II let the Avars attack the Slavs from Roman territory, they soon noted where the most booty was to be had. To make matters worse, Justin II started the Roman-Persian War of 572–591, which tied down forces in the east while they were needed in the Balkans. Maurice's predecessor and father-in-law, Tiberius II Constantine, emptied the treasury. For all those reasons, the Slavic incursions in the Balkans continued.
A few months before Maurice's accession in the winter of 581/2, the Avar Khagan Bayan, aided by Slavic auxiliary troops, took Sirmium, a large fortified settlement south of the Danube. By doing this, Bayan established a new base of operations within Roman territory from where he could raid anywhere in the Balkans unhindered. The Avars were not compelled to leave the territory until the Romans agreed to pay 80,000 solidi annually. The Slavs, partially under Avar rule, were not bound by the treaty and continued to pillage south of the Danube, which made the Avars and Slavs to be quite different threats.
Avar and Slavic incursions (582 to 591)
In 583, the Avars demanded an increase in the tribute to 100,000 solidi. Maurice decided to end all tribute to the Avars, as he concluded that additional concessions would only provoke additional demands. The renewed Avar invasion began in 583 with the capture of Singidunum after stiff resistance. The Avars quickly moved east and captured Viminacium and Augustae, and they began attacking as far southeast as Anchialus after only three months of war. A Roman embassy met the Avars near Anchialus, but negotiations broke down after the Avar Chagan threatened further conquests, provoking an irate response out of Comentiolus, one of the Roman ambassadors. Nevertheless, Maurice established peace in 584 by agreeing to pay the Avars' initial demands of 100,000 solidi. However, the Slavs were unhindered by the treaty and began to raid further south into Greece, as is evidenced by many coin hoards in the region, particularly in Attica near Athens and in the Peloponnese.
As Maurice's forces were tied down in a war against the Persians caused by Justin II, (see Roman-Persian Wars for details), he could muster only a small army against the Avars and Slavs who were marauding in the Balkans. His efforts were hampered by the fact that operations in the Balkans were a completely defensive matter. As opposed to the Persian theatre, the Balkan theatre provided little possibility for a soldier to bolster his pay by pillaging, which made fighting there rather unattractive. Maurice's badly-motivated troops found it difficult to achieve even minor and local success. Rather an exception, a victory won by Comentiolus at Adrianople 584/585 deflected Slavic incursions to southern Greece. The evident destruction of vast parts of old Athens probably happened around then.
Later on, the Balkans deteriorated in such a manner that in 585, the Persian shah, Hormizd IV, could reasonably hope to negotiate a peace treaty that would leave Armenia to the Persians. Maurice rejected the offer and was able to negotiate much more favorable peace terms in 591, after substantial successes on the battlefield. For the time being, however, he had to abide by Avar and Slavic incursions and hope that his forces garrisoned at Singidunum could deter the invaders, who posed a constant threat to the Avar homeland, just on the other side of the Danube. The Roman presence at Singidunum was strong enough to effect constant ends of Avar raids. However, it could not prevent the attacks.
Despite the Roman garrison at Singidunum, the Avars destroyed the fortified towns of Ratiaria and Oescus, on the Danube, and besieged Thessaloniki in 586, which were accompanied by Slavic raids down to the Peloponnese. Under the leadership of Comentiolus, the outnumbered Roman Army avoided any direct confrontation and restricted itself to disturbing the Avar raids by skirmishes and night attacks, a tactical expedient that was advised by Maurice's Strategikon. In 586 and 587, Comentiolus won several victories against the Slavs on the Lower Danube and nearly caught the Avar Khagan Bayan twice. At Tomis, on the shores of the Black Sea, the Khagan escaped via the lagoon-shaped coast, but an ambush on the south slope of the Balkan Mountains was thwarted by miscommunication among the Roman troops:
The following year, Priscus took over command from Comentiolus. His first campaign in Thrace and Moesia turned out to be a fiasco, even encouraging the Avars to advance as far as the Marmara Sea. As the state of the Avar bridges across the Sava river near Sirmium deteriorated, however, Avar pressure decreased.
Even so, Maurice did all he could to reinforce his troops on Balkans, as Slavic pillaging continued. He hoped to acquire more money by cutting the soldiers' payment by a quarter. Announcing the plans led to a mutiny on the Persian front in 588, which forced Maurice to abandon the idea. As a consequence, in the Balkans Maurice had only limited means to keep the Avars and Slavs at bay for the next three years.
Campaigns in 591 to 595
In the late summer of 591, Maurice finally made peace with Persian Shah Khosrow II, who ceded most part of Armenia to the Roman Empire. Finally, the veterans of the Persian wars were at his disposal and so was the recruiting potential of Armenia. Decreasing Avar and Persian pressure enabled the Romans to focus on the Slavs in 590/591. Maurice had already visited Anchialos and other cities in Thrace personally in 590 to oversee their reconstruction and to boost the morale of his troops and the local population. After making peace with Persia, he sped up that development by redeploying troops to the Balkans.
In 592, his troops retrieved Singidunum, but it was to be lost to the Avars again. Smaller Roman units were involved in policing actions against Slavic raiders in Moesia, re-establishing lines of communication between the Roman cities. Maurice aimed to re-establish a sturdy defense line along the Danube River, as Anastasius I had done a century earlier. Furthermore, he intended to keep the Avars and Slavs off Balkan territory by invading their homeland beyond Danube, to enable Roman troops to increase their earnings other than regular pay, by pillaging in hostile territory, which would make such campaigns more attractive.
General Priscus began to hinder the Slavs crossing the Danube in the spring of 593. He routed them several times before he crossed the Danube to carry on the fight in the uncharted swamps and forests of modern-day Muntenia, Romania until autumn. Then, he disobeyed Maurice's order to spend the winter on the northern Danube bank, among the frozen swamps and rivers and the leafless forests. Instead, Priscus retired to winter quarters in Odessos (modern Varna). That led to a new Slavic incursion 593/594 in Moesia and Macedonia, during which the towns of Aquis, Scupi and Zaldapa in Dobruja were destroyed.
In 594, Maurice disposed of Priscus and replaced him by his own rather inexperienced brother Peter. Despite initially failing, Peter maintained his position, defeated the Slavs (Priscus speaks about Bulgars) at Marcianopolis and patrolled the Danube between Novae (modern Svishtov) and the Black Sea. In late August, he crossed the Danube near Securisca west of Novae and fought his way to the Helibacia River, effectively disturbing Slav preparations for new pillaging campaigns.
That success enabled Priscus, who had meanwhile been entrusted with the command of another army upstream to prevent an Avar siege of Singidunum in 595 in a combined action with the Roman Danube fleet. The fact that the Avars retreated and gave up their plans to destroy the city and deport its inhabitants, as opposed to their conquest of 584, showed their lack of confidence and the threat they saw in the border fortress.
Subsequently, the Avars turned off to Dalmatia, where they sacked several fortresses, avoiding direct confrontation with Priscus. Roman commanders were never unduly concerned about barbarian incursions into that remote and impoverished province and so Priscus had to act cautiously. He could not afford to neglect the defence of the Danube and so he dispatched a small force to check the Avar advance. The small force hampered the Avar advance and even retrieved part of the booty.
Quiet interlude (596–597)
After that only moderately successful Avar raid into Dalmatia, there were only minor actions in the Balkans for about one-and-a-half years. Discouraged by the lack of success, the Avars saw more prospect for booty in the West and so raided the Franks in 596. Meanwhile, the Romans used Marcianopolis, near Odessos, as a base of operations on the lower Danube against the Slavs and failed to exploit the Avar absence. No major Slavic raids took place meanwhile.
Renewed campaigns (597–602)
Strengthened by Frankish pay-offs, the Avars resumed their Danubian campaigns in autumn 597, which surprised the Romans. The Avars even managed to besiege Priscus' army in Tomis. On 30 March 598, however, they lifted the siege, as Comentiolus had led an army of rather inexperienced soldiers over the Haemimons and was moving along the Danube up to Zikidiba, near modern-day Medgidia, just 30 kilometres (19 mi) from Tomis. For reasons that remain unknown, Priscus did not pursue the Avars and aid Comentiolus. The latter was forced to retire to Iatrus, where his troops were nonetheless routed and had to fight their way south over the Haemus Range. The Avars used the victory to advance to Drizipera, near Arkadiopolis, between Adrianople and Constantinople, where a large part of their army and seven sons of the Avar Khagan were killed by the plague.
Comentiolus was temporarily relieved of his command and replaced by Philippicus, and Maurice summoned the Circus factions and his own bodyguards to defend the long walls west of Constantinople. For the time being, Maurice had managed to buy off the Avars, and in the same year, a peace treaty was concluded with Bayan, the Avar Khagan, explicitly allowing Roman expeditions in Wallachia. The Romans used the remainder of the year to reorganize their forces and analyze the causes of failure.
Then, the Romans violated the treaty: Priscus advanced in the area surrounding Singidunum and wintered there in 598/599. In 599, the armies of Priscus and Comentiolus moved downstream to nearby Viminacium and crossed the Danube. On the north bank, they defeated the Avars in open battle in their own homeland. That was not only the first Avar defeat in their own homeland, but also saw the death of several more sons of Bayan Khagan. Priscus then thrust north into the Pannonian plain, the Avar homeland. He defeated the Avars deep within their realm, but Comentiolus remained near the Danube. Afterwards, Priscus devastated vast tracts of the land east of the Tisza, much in the same way the Avars and Slavs had done in the Balkans. Several Avar tribes and their Gepid subjects suffered particularly high casualties. Two other battles on the banks of the Tisza meant further Avar defeats.
Furthermore, the Exarch of Ravenna Callinicus repulsed Slav attacks on Istria in 599.