Tomislav (910–928) became king of Croatia by 925. The chief piece of evidence that Tomislav was crowned king comes in the form of a letter dated 925, surviving only in 16th-century copies, from Pope John X calling Tomislav "rex Chroatorum". According to "De Administrando Imperio", Tomislav's army and navy could have consisted approximately 100,000 infantry units, 60,000 cavaliers, and 80 larger ("sagina") and 100 smaller warships ("condura"), but generally isn't taken as credible. According to the palaeographic analysis of the original manuscript of "De Administrando Imperio", the estimation of the number of inhabitants in medieval Croatia between 440 and 880 thousand people, and military numbers of Franks and Byzantines - the Croatian military force was most probably composed of 20,000-100,000 infantrymen, and 3,000-24,000 horsemen organized in 60 allagions. Croatian Kingdom as an ally of Byzantine Empire was in conflict with the rising Bulgarian Empire ruled by Tsar Simeon I. In 923, due to a deal of Pope John X and a Patriarch of Constantinopole, the sovereignty of Byzantine coastal cities in Dalmatia came under Tomislav's Governancy. The war escalated on 27 May 927, in the battle of the Bosnian Highlands, after Serbs were conquered and some fled to the Croatian Kingdom. There Croats under leadership of their king Tomislav completely defeated the Bulgarian army led by military commander Alogobotur, and stopped Simeon's extension westwards. The central town in the Duvno field was named Tomislavgrad ("Tomislav's town") in his honour in the 20th century.