population are not fully elucidated. The Croats broke through the defensive lines on the Danube and began to gradually settle in the aforementioned Roman provinces at the end of the 6th, and especially at the beginning of the 7th century. Constantine VII records that they came at the invitation of Emperor Heraclius to defend the empire from the Avars, in which they were successful. In the conquered area they established their own kingdom. Pope John IV, himself a Dalmatian from the city of Salona, ​​in 640 sent a mission with Abbot Martin to redeem the captured natives from the Croats. Archbishop Grgur notes that at the end of the 8th century, the area of today's Tomislavgrad was in the center of the then Croatian state. Namely, he writes in his chronicle that in the time of King Budimir, a magnificent national assembly was held in Duvno in which the papal envoys took part. The Croatian king was crowned at the assembly, who at the same time divided the kingdom into administrative provinces. Duvno was on the border between the province of Red Croatia in the east and White Croatia in the west. Dominik Mandić maintains that the assembly was held around 753, however, the Archbishop of Bar dates the reign of King Budimir from 887 to 917, which would mean that the assembly was held in 885 or 886. Ivan Kukuljević Sakcinski argued that Budimir was in fact Tomislav of Croatia. Other historians dispute that the assembly was held at all, calling into question the credibility of the Chronicle. The end of the 8th century for Croatia and the area of Duvno was marked by significant changes. Charlemagne defeated the Avars in 796 and established the rule of the Frankish Empire in Croatian territories, so his empire now bordered Byzantium. Charles recognized the supreme authority of Byzantium over Venice and the Dalmatian city-states. This had significant consequences for areas outside Dalmatian cities inhabited by Croats. The Frankish political system was also being introduced in these areas and Frankish Christian missionaries have been active in these areas since the 9th century. Unlike other peoples who inhabited the Roman provinces and established their quasi-states, the Croats built an autonomous and respectable state organization during the 9th century. In the 10th century, the most important Croatian ruler was Tomislav. There are not many sources about his rule. During this period, Constantine VII wrote