7. – Bulgaria at the time of Krum and Omortag.

After King Krum (802 - 814) had conquered the Avars who, about 805, had been vanquished by the Franconians, he added to Bulgaria the territory lying east of the river Theiss (the present east Hungary and Transylvania), by which the Bulgarians became immediate neighbours of the Franconians and Moravians. During Krum's reign were furthermore aggregated to Bulgaria the territories south of the middle Danube, the districts of Branitschewo and Belgrade. In the course of continuous wars waged against Byzantium, Krum conquered the town Serdika (the Sofia of to day) with all its province and devastated the district of Adrianople as well as the surroundings of Constantinople. These wars were ended by a treaty agreed in 814-815, after Krum's death, by his son and successor Omortag (814-831).

By this treaty a small territory east of the river Tundja was adjudicated to Bulgaria. On this side the frontier lowered itself therefore from the middle of the ditch of Erkissija between the rivers Tundja and Tschoban Asmak to the Sakar Mountains from whence it ran west, and ended in a south-eastern direction at the present village Usundjowo; from there it drew along the slope of the Rhodope mountains to the Rilo Mmuntains, then farther, past the towns Dubnitza and Radomlr to the Sucha mountain and to the middle part of the Morava, and from this river again north-west to the river Kolubara. Later on, but still during the reign of Omortag, the Bulgarians succeeded by a convention with the Franconians to expand their dominion over the country between the lower courses of the Sava and the Danube – the Srem province – and to secure for themselves the possession of the old city of Singidunum at the mouth of the Sava, which henceafter was called Belgrad (Servia's present capital).

This map shows the frontiers of Bulgaria under Krum and under Omortag.