August 15, 718 the Arabs lift the siege of Constantinople. As a result of the battle, Byzantium was saved from defeat, and South-Eastern Europe was saved from the Arab invasion. The ancient chroniclers recognize the decisive help of the Bulgarian army under the leadership of Khan Tervel.
The siege of Constantinople in 718 was the second large-scale campaign of the Arabs after 674 to conquer the capital of Byzantium. At that time, only 95 years after the emergence of Islam, the Arab territories spread over three continents - Asia, Africa and Europe. The former Byzantine provinces of Syria, Palestine, Egypt and North Africa were conquered. At the beginning of the 8th century, the Visigothic Kingdom in Spain was also conquered. The Arabs are now really threatening Europe through a second wedge, by capturing the Roman capital of Constantinople.
Thus, in the autumn of 717, a huge Arab army marched towards Constantinople and besieged it from all sides. In this situation, the new ruler Leo III Isaurus sent envoys to the Bulgarian Khan Tervel with a request for help. Asparukh's successor showed remarkable statesmanship. Only 36 years have passed since the foundation of the Bulgarian state, during which Byzantium waged continuous wars against the young Bulgaria. Tervel reckons that the Arab invasion will not stop with the fall of Constantinople, and that this threat is much more formidable than Byzantium. He therefore accepted Constantinople's request for help.
Khan Tervel led the Bulgarian troops and reached near Constantinople. Already at the beginning of the hostilities, the Bulgarians defeated a 4,000-strong Arab detachment, personally commanded by the Arab leader Maslama ibn Abdel - Malis.
Subsequently, by order of Maslama, the Arabs from this side of the Bosphorus built two defensive ramparts - one against Constantinople and one to the west against the Bulgarians, with which to secure the rear of a 20,000-strong army. However, the ramparts did not save this 20,000-strong army from the Bulgarian troops.
Blocked by the Bulgarians on land, the Arabs spent an extremely hard winter, and many of them died of disease and hunger. In the spring of 718, Khan Tervel inflicted another defeat on the Arabs. Maslama's land army is defeated. On August 15, 718, the Arabs lifted the siege and withdrew from Constantinople. The fleet was overtaken by sea storms and only five ships reached Syria.