Answer
Repelling Umayyad sieges stands as one of Leo III's notable military triumphs. In 717-718, the Umayyad Caliphate, led by Caliph Sulayman ibn Abd al-Malik, launched a massive assault on Constantinople, the capital of the Byzantine Empire. Leo III skillfully organized the city's defenses, utilizing Greek fire, a devastating incendiary weapon, to repel the naval attacks.