imperial throne in 717 and had to cope with a large-scale Arab assault against Constantinople. In the summer of 717 the Arab general Maslama blockaded the Basileuousa (appellation of Constantinople meaning 'regnant') by land and sea. However, the Emperor's military expertise, the epidemics that hit the Arabic camp and the wide use of 'Greek fire' on the part of the Byzantines were the basic factors that contributed to the final defeat and retreat of the Arabic land forces a year later (718), and, eventually, to the destruction of their fleet.
The victory of the Byzantines over the Arabs in 717 was of primary importance, since this prevented their penetration into Europe from the southeast. Of equal importance was the victory of Charles Martel against the Arabs at Poitiers in France in 732, which also averted Arabic expansion into Europe. Under the following Isaurian Emperors, despite internal disorders due to the iconoclastic movement and other external enemies, there were further victories against the Arabs. Both Constantine V and his successor Leo IV won important victories. Not until the years of the last representatives of the dynasty, of Constantine VI and Irene, did the Arabs manage, after a series of successive raids into Asia Minor, to return after having accorded favourable peace conditions (783).