Khan (Kanas) Tervel (r. 700-718 AD, 700-721 according to some sources) was the emperor (bearing the Bulgar title khan or kanas) of Bulgaria at the beginning of the 8th century. He was the second ruler of the so called Danube Bulgaria, i.e. the First Bulgarian Empire (680-1018 AD), after the center of the Bulgarian state founded in 632 AD by his grandfather Khan Kubrat in what is modern-day Ukraine shifted towards the Balkan Peninsula.
In 705 AD, Byzantine Emperor Justinian II named Bulgaria’s Khan Tervel Caesar, the first foreigner to receive this title. Khan Tervel was probably a Christian like his grandfather Khan Kubrat and potentially his father Asparuh. His reign is known first and foremost for two major developments. First, in 705 AD, Tervel helped deposed Byzantine Emperor Justinian II regain his throne; as a payback, Byzantium ceded to Bulgaria the region then known as Zagore, which is the area around today’s city of Stara Zagora. This was the first territory south of the Balkan Mountain in what is today Southern Bulgaria that was formally obtained by the Bulgarian state which at the time included the territories on both sides of the Lower Danube. Second, in 717-718 AD Khan Tervel’s Bulgaria intervened during Constantinople’s siege by the Arabs from the Umayyad Caliphate on the side of Byzantium soundly defeating the Arabs.
The Constantinople Battle halted what was a major Muslim invasion of Europe. It is likened in importance to the Battle of Tours (or Battle of Poitiers) in which the Frankish King Charles Martel defeated the Umayyad Caliphate’s second attempt for a land invasion into Europe. The victory at Constantinople has earned Khan Tervel the title of “defender of Europe” in later historical accounts.