Tomislav (, ) was the first king of Croatia. He became Duke of Croatia and was crowned king in 925, reigning until 928. During Tomislav's rule, Croatia forged an alliance with the Byzantine Empire against Bulgaria. Croatia's struggles with the First Bulgarian Empire eventually led to war, which culminated in the decisive Battle of the Bosnian Highlands in 926. In the north, Croatia often clashed with the Principality of Hungary; the state retained its borders and, to some extent, expanded with the disintegrated Lower Pannonia. Tomislav attended the 925 Council of Split, convened by Pope John X, to discuss the use of Slavic languages in liturgy, and ecclesiastical jurisdiction over both Croatia and the Byzantine Theme of Dalmatia. Although the Pope sought to prohibit Slavic liturgy, the council did not agree. Jurisdiction over the region was given to the Archbishop of Split instead of Bishop Gregory of Nin. Since historical information on Tomislav is scarce, the exact years of his accession and death are unknown. The reigns of his successors were marked by a series of civil wars in Croatia and a gradual weakening of the country. Reign Duke of Croatia Although Tomislav's ancestry is unknown, he might have been a member of the Trpimirović dynasty. There is a nearly twenty-year difference between the first documentation of Tomislav and the last mention of Muncimir, his predecessor as Duke of Croatia. Historical records of Tomislav are scarce, but it is assumed that he was a son of Muncimir. Tomislav succeeded Muncimir, son of Trpimir I, as duke in (the most widely-accepted view) or after others ruled following Muncimir's death. In any case, Tomislav came to the Croatian throne some time between 910 and 914. In Historia Salonitana (History of Salona), a 13th-century chronicle by Thomas the Archdeacon of Split, Tomislav was mentioned as duke of Croatia in 914. After the Hungarian conquest of the Carpathian Basin in the late 9th and early 10th centuries, the Hungarians immediately began raiding and expanding their territory. They threatened Lower Pannonia (still nominally under Frankish suzerainty) and killed Braslav, the last Pannonian duke. The Hungarians also fought Croatia, although it was not a primary target of their raids. The Chronicle of the Priest of Duklja mentions that Tomislav, the length of whose rule was specified as 13 years, successfully fought the Battle of Drava River with the Hungarians. Since the Venetian chronicler Andrea Dandolo and