August 15, 718 the Arabs lift the siege of Constantinople. As a result of the battle, Byzantium was saved from defeat, and Southeastern Europe was preserved from the Arab invasion. 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, Arab territories stretched across 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 were now really threatening Europe through a second wedge, capturing the Roman capital Constantinople.
So in the autumn of 717, a huge Arab army set out for Constantinople and besieged it from all sides. In this situation, the new ruler Leo III the Isaurian sent envoys to the Bulgarian Khan Tervel with a request for help. Asparuh's successor displayed remarkable statesmanship. Only 36 years had passed since the foundation of the Bulgarian state, during which Byzantium waged continuous wars against the young Bulgaria. Tervel estimated that the Arab invasion would not stop with the fall of Constantinople and that this threat was much more terrible than Byzantium. Therefore, he accepted Constantinople's request for help.
Khan Tervel led the Bulgarian troops and reached the vicinity of Constantinople. At the very 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 difficult winter, with many of them dying of disease and hunger. In the spring of 718, Khan Tervel inflicted another defeat on the Arabs. Maslama's land army was defeated. On August 15, 718, the Arabs lifted the siege and withdrew from Constantinople. The fleet was caught up in sea storms and only five ships reached Syria.