A talented commander and a deft diplomat this is how historians describe the son of Asparukh and second Bulgarian ruler. It is disputed whether Tervel ascended the throne in 700 or 701 after Asparukh was presumably killed in a battle with the Khazars. He ardently continued his father's lifework. The Byzantine emperors bitterly regretted that they had allowed a pagan state to form in the empire's lands north of the Balkan range. And the empire was being weakened by internecine feuds for the throne and was suffering defeats in wars with the Arabs. As soon as he ascended the throne, Khan Tervel focused his attention on the southern border where Byzantium no longer posed as grave a threat as it used to. In the involved relations with the empire he applied the power of the sword and the wiliness of diplomacy with equal deftness. He persistently pursued his major purpose: to expand the territory of the new state and to establish himself as an independent ruler. His abilities as a statesman and the developments in the neighboring Byzantium allowed him to achieve both.
In 705 Khan Tervel's army helped Emperor Justinian II to regain his throne. The grateful basileus welcomed the Bulgarian Khan in Constantinople with great honors, putting a royal mantle on his shoulders and showering him with gifts. Khan Tervel and Emperor Justinian stood together as equals at the parade of Byzantine troops. And best of all, under the new treaty Bulgaria received, for the first time, lands south of the Balkan range: the region of Zagora in Eastern Thrace, through which many strategic routes passed. Furthermore, the Khan was awarded the title of Caesar, making him second only to the emperor. This was the first time in Byzantine history that a foreigner was bestowed such a title, and a lead seal reading "Mother of God, help the Caesar Tervel" attests to the honor.
The Khan, however, was not lulled by the honors he knew the waywardness of Byzantine rulers all too well. When three years later Justinian II marched on Zagora in an attempt to recapture it, Tervel routed him near Anchialo (Pomorie), taking many prisoners and weapons. Twice more the Byzantine army was put to flight and after successful raids into Thrace in 712, Tervel reached the walls of Constantinople. This is when the dream of Bulgaria's medieval rulers was born: to enter the Byzantine capital in triumph.
With the conclusion of the famous treaty of 716, Khan Tervel took the first step to make the dream come true.
The treaty placed the border between Bulgaria and Byzantium in Thrace, and Bulgaria kept the region of Zagora. Defeated and humiliated, Byzantium was committed to pay annual tribute to Bulgaria.
Khan Tervel was the first medieval ruler of Bulgaria to understand that living next to Byzantium called for some mutually beneficial cooperation as well. He came to the aid of the basileus when, in 718, Arabs stormed the walls of Constantinople for the third time. "The Bulgars assaulted the Arabs, slaying many of them... They were more afraid of the Bulgars than of the Byzantines," reads the account of an Arab chronicler of Khan Tervel's sweeping victory which left some 30,000 Arabs dead. Bulgaria was one of the few European states to stand in the way of the Arab invasion of Europe.
At the same time Khan Tervel was striving to consolidate his state. His rule was marked by a growing prosperity of both the Khan and the people, and a Byzantine chronicler would later write of the wealthy ruler: "Tervel, commander of the Bulgars, was at the apogee of his prosperity... He would turn the shield he used in times of war hollow side up, put his whip onto it and pour money until both were covered. He would put his spear on the ground and pile silk garments at its two ends. He would fill boxes with gold and silver coins and give it out to the soldiers, throwing gold with his right hand and silver with his left."