The Byzantine–Hungarian War was a series of border conflicts between the Byzantine Empire and the Kingdom of Hungary that took place in the Balkans from 1149 to 1155. The conflict was affected by international disputes in Europe, primarily between Manuel I Komnenos and Roger II of Sicily, starting in the 1140s. The war broke out when Géza II of Hungary provided military assistance to the Serbs of Rascia (Raška), who rebelled against Byzantine suzerainty. The conflict ended with a peace treaty that restored the status quo ante bellum and established peace for five years. In 1161, the parties agreed to extend the truce for ten years but the relationship between them remained hostile, causing further clashes throughout the 12th century.
Background
Status quo
After the Byzantine–Hungarian War between 1127 and 1129, relations between the two powers had stagnated but no direct confrontation occurred for twenty years. During the war, the Byzantines retained control of Braničevo (Barancs), Belgrade and Zemun, and recaptured the Sirmium region, which had been Hungarian since the 1060s. Following the end of hostilities with Hungary, John II Komnenos was able to concentrate on Asia Minor for most of his remaining years. In the 1130s, Byzantine interests regarding Hungary were limited to maintaining the status quo from the 1129 treaty and to securing the empire's northernmost frontier along the Danube.
Béla II ascended the Hungarian throne in 1131. His blindness prevented him from administering his kingdom without assistance so he put his trust in his wife Queen Helena and her Serbian relatives, especially her brother Beloš. King Coloman's supposed son Boris Kalamanos attempted to dethrone Béla II. According to Byzantine historian John Kinnamos, Emperor John II Komnenos gave Boris a bride from his own family but the emperor refused to help Boris take the Hungarian throne.
Following Boris' first failure in 1132, Hungary adopted an expansionist policy. Under the influence of his Serbian courtiers, Béla II turned his attention to the Balkans. Bosnia appears to have accepted Béla's suzerainty without resistance by 1137; following this, Béla II and his descendants adopted the title King of Rama. Prior to that, Bosnia had been considered a Byzantine sphere of interest in the Balkans. Simultaneously, the Hungarians seized Split (Spalato) in Dalmatia, which was disadvantageous for the Byzantine Empire. John II Komnenos had to deal with the Norman conquest of southern Italy so he made an alliance with the Holy Roman Empire against the ambitions of Roger II of Sicily. In this context, the relationship between Hungary and the Byzantium remained intact. The remains of Béla's father, former Hungarian pretender Prince Álmos, were returned from the Byzantine Empire to Hungary in 1137, supporting the existence of a permanent connection between the realms.
European perspective
Following the death of Béla II, his eleven-year-old son Géza II ascended to the Hungarian throne in February 1141. During his minority, Géza's mother Helena and her brother Beloš ruled the kingdom. In April 1143, Manuel I Komnenos succeeded his father John II as Byzantine Emperor; Manuel was eager to restore his empire to its former status as the superpower of the Mediterranean, and pursued an energetic and ambitious foreign policy. The pretender Boris successfully approached Conrad III of Germany to seek his assistance against Géza at the end of 1145, which worsened Hungary's relationship with the Holy Roman Empire. The following year, the conflict escalated into the Battle of the Fischa between the Hungarians and the Germans, the Austrians and the Bohemians after Boris' defeat. Disputes among European powers led to the formation of two coalitions in the late 1140s. One alliance was formed by Emperor Manuel and Conrad III against the Normans and their king Roger II of Sicily. Because of their cooperation, Hungary was in a difficult situation and experienced foreign-policy isolation. Géza II sided with Roger II and his allies, including the rebellious German prince Welf VI and Uroš II of Serbia. The pretender Boris attempted to take advantage of Conrad III's decision to lead the Second Crusade to the Holy Land through Hungary. In 1147, German crusaders marched across Hungary without major incident, and King Louis VII of France and his crusaders arrived in Hungary in August of that year. Louis VII rejected Géza's demand to extradite Boris, whom he held in custody and took him out of Hungary. Boris settled in the Byzantine Empire.
Taking advantage of Conrad's crusade, which captured Manuel's attention, the Normans invaded; in 1147, they seized Corfu, and plundered Thebes and Corinth. The following year, Manuel was distracted by a Cuman attack in the Balkans; he enlisted the alliance of Conrad III of Germany and the help of the Venetians, who quickly defeated Roger II of Sicily with their powerful fleet. By 1148, the political situation in the Balkans was divided into the alliance of the Byzantines and Venice, and that between the Normans and Hungarians. The Serbs, Hungarians and Normans exchanged envoys because it was in the interest of the Normans to stop Manuel's plans to recapture Italy. Manuel agreed with Conrad on a joint invasion and partition of southern Italy and Sicily. While Manuel was in Valona (today Vlorë, Albania) planning an offensive across the Adriatic Sea, the Serbs under Uroš II—who was also a maternal uncle of Géza II—revolted, threatening Byzantine Adriatic bases and forcing Manuel to interrupt his preparations for an invasion of Southern Italy and instead invade the Grand Principality of Serbia (also known as Rascia) in 1149. At the same time, the revolt of Welf VI, which was also financed by Roger II and Géza II, and the rise of Henry the Lion, forced Conrad III to stay in the Holy Roman Empire between 1149 and 1151.
The alliance between Manuel and Conrad III was not directed against Hungary but Géza II participated in the Roger-led coalition against the two emperors because German–Hungarian relations had been hostile since 1146 and the Byzantines strongly opposed Géza's foreign policy, including his support of Rascia, his involvement in the internal conflicts of the Kievan Rus' and his cooperation with Louis VII of France. Iziaslav pursued an anti-Byzantine policy and expelled the metropolite from Kiev to end the ecclesiastical suzerainty of the Patriarch of Constantinople over the Kievan Rus'. Géza's support contributed to the weakening of Byzantine influence in the Rus' principalities. The relationship between Hungary and the Byzantium was also negatively affected by the Byzantine Empire granting asylum to Boris.
Border clashes
Serb revolt
[Manuel]... did not desire to turn back. He ordered [John] Kantakouzenos...to advance further and engage the barbarians... John [Kantakouzenos]... struck the grand župan [sic!] Bakchinos [Bágyon] on the back... Bakchinos himself and his followers... assailed the emperor at a run...After a long engagement, Bakchinos struck, bringing down his sword on the emperor's jaw, yet was unable to cut the screen [of chain mail] which hung from the helmet over the eyes. The blow, however had enough force that the rings placed next to the flesh were deeply impressed on it... In this struggle Kantakouzenos was deprived of two fingers of one hand. Leading about forty of the enemy captive, the emperor returned to camp.
The emperor [Manuel], apprised that the ruler of Serbia was once again working wickedness in the mountains... marched against them with little preparation, as he deemed them unworthy opponents in battle. But the Serbs, emboldened by the support of a large body of Hungarian allied forces, put up a much stiffer resistance than expected. Ever steadfast, John Kantakouzenos engaged the barbarians in close combat, giving and taking blows until he lost the fingers of his hands. The emperor himself fought a duel with the grand zupan [sic!] Bakchinos [Bágyon] a man of heroic stature and brawny arms who struck a blow that shattered the iron screen dependent from the helmet that protected the emperor's face and eyes. The emperor, in turn, severed Bakchinos's arm with his sword, rendering him helpless, and took him captive.
When the Serbs of Rascia rebelled against the Byzantine Empire in 1149, Manuel sent a retaliation force to crush the rebellion. At the end of September that year, Manuel commanded the imperial army, which entered Rascia from the Adriatic coast across Pelagonia. Uroš II ordered his people to withdraw to the mountains to avoid direct confrontation. The emperor's troops pillaged the region, devastating Serbian towns and abducting inhabitants but Manuel was unable to capture Uroš and his courtiers. Despite that, Manuael returned home and held a victory march in Constantinople at the end of 1149.
There is an argument the Hungarians did not directly take part in the Byzantine–Serbian conflict of 1149; neither John Kinnamos nor Niketas Choniates mentioned them in their accounts of Manuel's invasion. The Volhynian annals refer to Géza's statement in August 1149; " ... I am engaged in war with the emperor [Manuel]". The Hypatian Codex says Géza referred to his war against Manuel when excusing himself for refusing to send reinforcements to Iziaslav II, whom Yuri Dolgorukiy, Prince of Suzdal, expelled from Kiev in August 1149. Historians who say Hungary did not participation in the Serbian revolt argue the monarch referred to his membership in the Norman-led coalition against the Byzantine Empire, which he considered his enemy. According to the triumphal poem of the emperor's panegyrist Theodore Prodromus, Hungarian forces supported the Serbs during the emperor's campaign.
Following his unilaterally declared victory, Manuel again prepared to invade the Kingdom of Sicily in early 1150. Despite the Battle of Flochberg, in which Conrad III defeated the rebellious Welf VI, Conrad did not join Manuel's cause because he felt threatened by a proposed French–Norman crusade to the Holy Land. The Serbs remained hostile to Byzantine interests in the Balkans. Manuel led another campaign against the Serbs in late 1150. Géza II sent a strong force of Hungarians, Pechenegs and Khalyzians (Muslims) to support Uroš II. From Niš, Manuel, alongside John Kantakouzenos and John Doukas Komnenos, marched towards the Sava river, where his army unsuccessfully tried to prevent the Serb army from uniting with the Hungarian auxiliaries led by comes Bágyon (or Bacchinus). After brief skirmishes, the Byzantine army won the Battle of Tara against Serb–Hungarian forces near the Tara river. According to Kinnamos, Manuel dueled with Bágyon after Kantakouzenos lost his fingers during the battle. Following the battle, Uroš II swore loyalty to Manuel and his principality again became a vassal of the Byzantine Empire.
Manuel's retaliatory campaign
[...] When he [Manuel] reached the Danube's shore, the ships which he had prepared in Byzantion were not at hand...he boarded a skiff, such as the wooden ones which lie by the shores there, and hastened to the farther shore [of the Sava]; he himself held his horse towed by the bridle.
..the emperor [Manuel] hastened to attack the Hungarians while still dripping with hot sweat and before he had wiped the dust from his face. He resented the assistance they had given the Serbs, and he decided to take advantage of the absence...the Hungarian king [Geza II]... warring against the neighboring Rhos [Rus']. Crossing the Sava River, he burst in upon Frangochorion [Syrmia] (this is not the least part of Hungary but a sufficiently populated one, situated between the Istros [Danube] and Sava rivers, in which a mighty fortress called Zevgminon [Zemun] had been built) and ravaged the land.
According to John Kinnamos, the Byzantine army returned to Constantinople after the subjugation of the Serbs and then launched a retaliatory expedition against Hungary. According to Niketas Choniates, Manuel continued his military campaign immediately after his victory in the Battle of Tara. Niketas says at the time of Manuel's invasion, Géza II was warring in the Kievan Rus'. His report is confirmed by the narrative of German chronicler Henry of Mügeln. The chronology is uncertain; most historians believe Manuel advanced into Syrmia (Sirmium) in the final quarter of 1151, while others put the date of attack in 1152. Ferenc Makk, based on a speech by Michael of Anchialus from 1155, said the conflict escalated into a war between the empire and Hungary in late 1150 or early 1151, which accords with all Byzantine, Russian and German chronicles. According to János B. Szabó, Manuel's campaign took place in mid 1152.