The Second Arab Siege of Constantinople began in 717, led by the Umayyad general Maslama ibn Abd al-Malik. This campaign was a significant part of the Arab-Byzantine Wars, as the Umayyad Caliphate sought to extend its dominion into the Balkans and Europe by capturing the Byzantine capital. This ambitious siege came on the heels of a previous unsuccessful attempt in 674-678, and planning for the operation involved meticulous strategic considerations including the building of a siege armada and the mobilization of thousands of troops along with heavy equipment for assaulting fortified positions.

During the siege, Maslama's forces blockaded the city by land and sea, aiming to cut off its supplies and reinforcements. The Byzantines, under the leadership of Emperor Leo III, were resolute in their defense. They utilized innovative tactics, such as Greek fire, a potent incendiary weapon that proved effective against the besieging forces. The defenses of the city, which included thick walls and a strong naval presence, made it difficult for the Arabs to sustain their assault. The prolonged siege would last nearly a year, with intense combat and heavy losses on both sides.

Despite the military prowess of the Umayyads, the combination of resourceful Byzantine defenses, internal dissent within the Arab ranks, and weather-related challenges ultimately led to the failure of the siege. By 718, the efforts of the Byzantine defenders, together with the arrival of reinforcements and the harsh winter, forced Maslama to retreat. This also marked a turning point in Byzantine-Arab relations and laid the groundwork for future encounters between the two empires.