Omurtag the Builder

Krum's successor Khan Omurtag (r. 814–831) concluded a 30-year peace treaty with the Byzantines, thus allowing both countries to restore their economies and finance after the bloody conflicts in the first decade of the century, establishing the border along the Erkesia trench between Debeltos on the Black Sea and the valley of the Maritsa River at Kalugerovo. 

To the west the Bulgarians were in control of Belgrade by the 820s and the northwestern boundaries with the Frankish Empire were firmly settled along the middle Danube by 827. To the north-east Omurtag fought the Khazars along the Dnieper River, which was the easternmost limit of Bulgaria. Extensive building was undertaken in the capital Pliska, including the construction of a magnificent palace, pagan temples, ruler's residence, fortress, citadel, water-main, and bath, mainly from stone and brick. Omurtag started in 814 persecution of Christians, in particular against the Byzantine prisoners of war settled north of the Danube. The expansion to the south and south-west continued under Omurtag's successors under the guidance of the capable kavhan (First Minister) Isbul.