A Byzantine–Hungarian War was fought between Byzantine and Hungarian forces on the Danube between 1127 and 1129. Byzantine primary sources, Cinnamus and Choniates, give little detail about this campaign; no dates are specified, and what they do say differs considerably. The chronology presented here, 1127–1129, follows that of Michael Angold and other scholars, but John Fine has the events taking place earlier in 1125–1126. According to the Byzantine chronicler Niketas Choniates, the citizens of the Byzantine town Braničevo "attacked and plundered the Hungarians who had come to" the Byzantine Empire "to trade, perpetrating the worst crimes against them." Stephen II of Hungary broke into the empire in the summer. His troops sacked Belgrade, Braničevo and Niš, and plundered the regions around Serdica and Philippopolis, before returning to Hungary. In response, Emperor John II marched against Hungary in 1128, where he defeated the royal troops in a battle at Haram, and "captured Frangochorion, the richest land in Hungary". Following his victory over the Hungarians John II launched a punitive raid against the Serbs. Dangerously for the Byzantines the Serbs had aligned themselves with Hungary. Many Serbian prisoners were taken, and these were transported to Nicomedia in Asia Minor to serve as military colonists. This was done partly to cow the Serbs into submission, and partly to strengthen the Byzantine frontier in the east against the Turks. The Serbs were forced to acknowledge Byzantine suzerainty once again. In Hungary, the defeat at Haram undermined Stephen II's authority and he faced a serious revolt when two counts, named 'Bors' and 'Ivan', were declared kings. Both were eventually defeated, Ivan being beheaded and Bors fleeing to Byzantium. Stephen was unable to participate in any of the fighting because he was sick, recuperating in his homeland, according to John Kinnamos. John Kinnamos wrote of a second campaign by Stephen against the Byzantine Empire, when the Hungarian troops, supported by Bohemian reinforcements under the command of Duke Václav of Olomouc, took Braničevo by storm and destroyed its fortress. The Hungarians had renewed hostilities, possibly in order that King Stephen could be seen to reassert his authority, by attacking the Byzantine frontier fortress of Braničevo, which was immediately rebuilt by John. Further Byzantine military successes – Choniates mentions several engagements – resulted in a restoration of peace. Cinnamus describes a Byzantine reverse occurring before peace was established, which suggests that the campaign was not entirely one-sided. Hungarian records, however, agree with Choniates in indicating that King Stephen was again defeated and was consequently forced to negotiate a peace on Byzantine terms. Historian Ferenc Makk thinks that Emperor John II Komnenos was forced to retreat and sue for peace and that the treaty was signed in October 1129. The Byzantines were confirmed in their control of Braničevo, Belgrade, and Zemun and they also recovered the region of Syrmia, which had been in Hungarian hands since the 1060s. The Hungarian pretender Álmos died in 1129, removing the major source of friction.
