Croatian – Bulgarian battle of 926 In 926 a battle was fought in the Bosnian highlands between the armies of the two Balkan rulers of the time : Bulgarian Tsar Simeon I , the great victor of the Battle of Anchialus over the Byzantine Empire ten years earlier , and King Tomislav of Croatia , the first king of the Croatian state . It was fought in the area of the highlands of Eastern Bosnia near the Drina River , the border area between the Kingdom of Croatia and the Bulgarian Empire . The Bulgarian ruler , Simeon , was a wise and able man with a restless and insatiable spirit . He spent his entire life fighting battles with neighboring countries . His basic aim was to defeat the Byzantine Empire and conquer Byzantium . To achieve his aim , Simeon overran the eastern and central Balkans several times , occupied Serbia and finally attacked Croatia . Battle . Events preceding the war . After long wars and great success , capturing a larger part of the Byzantine territory in Europe , Simeon the Great was crowned at the church of Ohrid as " Tsar of all Bulgarians and Greeks " by the newly appointed Bulgarian patriarch 925 . According to the juridical reasoning of the time , only the Pope and the Byzantine Emperor could bestow royal or imperial titles , and an emperor might be crowned only by a patriarch . Byzantine Emperor Romanus Lecapenus protested bitterly against Simeon ' s usurpation of the imperial title . The Patriarch of Constantinople , Nicholas Mysticus , did the same . In such a predicament , Simeon demanded Pope John X ( 914 - 928 ) send him an imperial crown and to recognize the head of the Bulgarian church as Patriarch . Naturally , Simeon had to promise to recognize the papal primacy in the Church . John X accepted Simeon ' s request and sent a solemn mission to Bulgaria , headed by Cardinal Madalbertus and John , illustrious Duke of Cumae . The papal mission reached Bulgaria at the end of summer or during the fall of 926 , carrying a crown and scepter with which they would crown Simeon as Bulgarian Emperor . When the papal mission arrived in Preslav , Madalbertus started long negotiations with Simeon and the representatives of the Bulgarian church . Probably , Madalbertus convoked a church synod in Bulgaria as he later did in Split , in Croatia , on his way back to Rome in 928 . The negotiations regarding ecclesiastical matters were successful , and Archbishop Leontius was created Patriarch in Preslav , still during Simeon ' s reign . Reasons for the war . Meanwhile , Simeon undertook imposing preparations for his crowning during the summer of 927 . All of a sudden , he decided to wage a war against the Kingdom of Croatia . The reason might have been that Tomislav received and protected the Serbs who were expelled by Simeon from Rascia . In all probability , however , the main reason was that Simeon , if crowned by the Papal Legate , feared an attack from the Byzantine Emperor supported by Tomislav . Emperor Romanus Lecapenus won the friendship of Tomislav some years previously , handing over the Byzantine Dalmatia to Tomislav and recognizing him as King of Croatia ( Pope John X recognized Tomislav as King of Croatia in 925 ) . During the summer of 926 , Tomislav sent his troops to Italy to expel Saracens from the city of Sipontus , which belonged to the Byzantine province of Langobardia . This event could have been a sufficient proof to Simeon that the Croats took the side of the Byzantine Emperor and that they would support him actively in the future . Therefore , when Simeon sent a great army against the Croats , the Bulgarians were met by Tomislav ' s army in the mountainous region of Eastern Bosnia . Battle . According to Byzantine historian Constantine Porphyrogenitus , King Tomislav was able to field an army of 100 , 000 foot soldiers , 60 , 000 horse soldiers and 80 battleships ( " disputed " ) . The strength of Simeon ' s army is unknown but was probably 30 , 000 - 70 , 000 . The commander of the Bulgarian forces in this battle was Duke ( Dux ) Alogobotur . The Croatian forces under the leadership of their king completely devastated the Bulgarian army . Key to Tomislav ' s triumph was likely the choice of terrain on which the battle took place : Croatian soldiers were probably more skilled in fighting in the mountainous terrain of the Bosnian highlands . The great military skill of the Croatian king and his cavalry was probably also a decisive factor against the Bulgarians . Aftermath . Fearing a Bulgarian retribution , Tomislav accepted to abandon his union with Byzantium and make peace on the basis of the status quo , negotiated by the papal legate Madalbert . Another consequence was , that a large part of Macedonia ( theme ) came again under Byzantine rule by a Peace agreement between the Bulgarians and the Byzantines in 927 , because between these two events was a causal context .