The founder of the Bulgarian state, khan Asparukh, was inherited from his son khan Tervel (701-721). In 704 the dethroned Byzantine emperor Justinian II asked the Bulgarian ruler for help. In 705 khan Tervel arrived outside the walls of Constantinople with 15000-strong cavalry and reinstated Justinian II to his throne. As a result of these endeavours the Justinian II granted Tervel the title of Caesar - the second title in Byzantium after the emperor's one, and gifted him with plenty of gold and jewelry. Besides Bulgaria got Zagore region to the south of the Balkan.

At the beginning of the 8th century a frightful menace threatened medieval Europe - the powerful Arabian caliphate. In the West, the fanatical warriors of Mohammed conquered the Iberian Peninsula. In the East the situation  was even more dramatic. About 716 the whole of Byzantium was trodden over by Arab cavalry and its capital squeezed in the steel belt of siege and starvation ready to surrender. The new Byzantine emperor Theodosius III again asked khan Tervel for help and again the Bulgarian heavy cavalry under the command of khan Tervel came forward at the walls of Constantinople. The war continued two years. In a crucial battle in 718 the Bulgarian cavalry defeated the Arab one. The rest of the Arab troops was finished off by the Bulgarians in the next couple of days. This blow put an end to the Arabs attempting to penetrate into Europe through the Balkans.

Bulgaria and Byzantium observed almost 40 years the peace treaty concluded in 716. However in the middle of the 8th century Bulgaria entered on a prolonged crisis period of intestine wars and frequent changes of the state rulers. At the same time Byzantium concentrated all its forces to destroy the Bulgarian state. In the course of 20 years (755-775) the Byzantine emperor Constantine IV carried out 9 campaigns against Bulgaria. At the cost of great efforts, the Bulgarians succeeded in withstanding the Byzantine aggression and lost only the region Zagore in Thrace which was gifted in the past to khan Tervel.

The end of the crises put khan Kardam (777-802). But the real upsurge of the Bulgarian state began under the next ruler - khan Krum.

There is a remarkable monument of that time which has become famous under the name of the Madara Horseman. That is a stone relief near the village of Madara represented a horseman who kill a lion by his spear. The relief is carved on a huge sheer cliff. Some historians assume that the monument depicts khan Tervel and that it is a symbol of the khan's power.