The only written source that describes in detail the Magyar conquest of the region in the late 9th century is the Hungarian literary work Gesta Hungarorum, written at the turn of the 12th and 13th centuries. Although its credibility has been questioned several times, there is no other written source that reports about the events that took place outside of Frankish Pannonia in connection with the Magyar conquest. The Gesta Hungarorum recounts that the Magyars invaded the Carpathian Basin through the Verecke Pass, and their first enemy was Laborec, a Slavic duke who had his seat at present-day Uzhhorod in Transcarpathia, Ukraine. “The count of the Ung castle, Loborc by name, who in their language was called duca…”. The ruler of a Bulgarian vassal principality, Laborec was the first local ruler that the Hungarians encountered. He was defeated and killed near Zemplín on the banks of the Laborec river that still carries his name. A Bulgarian ruler called Salan is a central figure in the Gesta. He is described as the most powerful among local rulers who “held so much power over his neigbours”. In the Gesta, he is challenged by Árpád, the most powerful chieftain among the Magyars, while the other chieftains conquer different territories.
After he was informed about the defeat of several of his vassals who were “taken in fetters to the castle of Ung”, Salan “sent envoys to Duke Árpád, saying that he should leave their land and start homewards to his native soil”. The Gesta continues that “Duke Árpád angrily replied to Salan”, instructing him to “to leave our land and go by the swiftest course to the land of the Bulgarians”. The inhabitants of Salan’s duchy submitted themselves to the Magyars in fear of them “such fear and dread overtook the inhabitants of the land that they cringed before duke Árpád and his leading men, like servants to their own lords” The author added that “Salan, when he learnt of the might and deeds of the Hungarians, feared lest at any time they, moved by wrath, should expel him from his realm” and asked for support from the Bulgarian tsar and the Byzantine emperor. When these troops arrived, he set out from his capital at Titel “with a raging mind to ride against Duke Árpád.” Árpád also led his army to battle, and the decisive battle was fought near present-day Tiszaalpár in Hungary. When describing the events, the author calls present-day Belgrade as Albam Bulgariae (“Bulgarian white castle”).
The armies of the two foes joined in battle and they began to fight each other fiercely and, when the whole army of Duke Árpád entered the fighting against the Greeks, very many Greeks and Bulgarians were slain. The aforesaid Duke Salan, when he saw his men weakening in battle, took to flight and hastened for safety to Albam Bulgariae [Belgrade]. The Greeks and Bulgarians, struck by fear of the Hungarians, forgot which way they had come and, turning to flight, sought to save their lives by swimming across the Tisza, thinking it a little river, but such fear and fright overcame them that for fear of the Hungarians nearly all were killed in the Tisza river, so that barely any remained to give the bad news to the emperor. And that place where the Greeks were killed is to this day now called the harbour of the Greeks [portus Grecorum].