Legend of Khan Tervel

Tervel is first mentioned in the Byzantine sources in 704, when he was approached by the deposed and exiled Byzantine emperor Justinian II.
In 705 with a big army of proto-Bulgarians and Slavs, khan Tervel headed for Constantinople and settled down in front of the so called Harsian door, which leaded to the way to Odrin.  Three days long Justinian II negotiated with the habitants of the capital but all he got for his promises was offences and mockeries. On the 4th day he succeeded to gain entrance into the city, conquered Constantinople and punished cruelly his enemies. The happy conqueror didn’t fall behind his promises and generously       returned the favor to the Bulgarian ruler. Justinian awarded Tervel with many gifts, the title of kaisar (Caesar), which made him second only to the emperor and the first foreign ruler in Byzantine history to receive such a title. The other privilege was the territorial concession he received, located in northeastern Thrace a region called Zagore and located between Sliven, Iambol and Black Sea.
In 708 the mounted troops crossed the territory of Thrace and the Byzantine fleet debarked at Ankhialo (Pomorie). Khan Tervel suddenly attacked and the Byzantine army was defeated again.
In 711 Justinian II faced a serious revolt in Asia Minor, his army declared for emperor its commander.  Justinian again was forced to seek the aid of Tervel . Justinian II was beheaded and the Bulgarian army returned to the motherland without any hindrance.
The instability of Byzantine and the impunity, typical of Tervel’s reign forced the Byzantine emperor Theodosius III to start peace talks. The contract was concluded in 716 and included 4 clauses:1) the border between the two countries should have passed along the so called Mileony area in Thrace 2) Bulgaria had to receive yearly interwoven with gold clothes and red leaders at the amount of 30 liters of gold. 3) The two countries had to extradit to each other the political escapees. 4) The goods passing through the border had to have special stumps and lead seals on it otherwise they had to be confiscated.
In the summer of 718 the Arabs attacked the Bulgarians but again were defeated. According to the Theophanes, the Bulgarians slaughtered some 22,000 Arabs in the battle before Constantinople. Аll these victories not only made Khan Tervel famous for his deeds but also made him more self-confident and  strong-willed, which for the 3rd time led him in front of the door of Constantinople.
 These are the last records about Khan Tervel. According to them he ruled for 21 years and died in 721.