The Byzantines were unable to respond effectively to the Muslim advance in Africa because the two decades between 695 and 715 were a period of great domestic turmoil. They did react with raids of their own in the East, such as the one in 709 against Egypt which captured the local admiral, but they also were aware of a coming onslaught: as Caliph al-Walid I (705–715) readied his forces for a renewed assault against Constantinople, Emperor Anastasios II (713–715) prepared the capital, and mounted an unsuccessful pre-emptive strike against the Muslim naval preparations. Anastasios was soon overthrown by Theodosius III (715–717), who in turn was replaced, just as the Muslim army was advancing through Anatolia, by Leo III the Isaurian (717–741). It was Leo III who faced the second and final Arab siege of Constantinople. The use of Greek fire, which devastated the Arab fleet, was again instrumental in the Byzantine victory, while a harsh winter and Bulgar attacks further sapped the besiegers' strength.