Emperor Leo III, the ‘Isaurian’, was indeed the man, and for the empire the hour was desperate. A brilliant soldier, strategist, diplomatist and spymaster, he was exactly what the Romans/Byzantines needed at this moment in their history. There is no doubt at all that the empire faced an existential threat from the ascendant Umayyad Caliphate; a hundred years after Mohammad burst out of the desert, the Muslim conquests seemed destined to win to their cause the whole world. Moreover, the early eighth century was a time of huge internal instability within the Byzantine Empire, even as the Arab threat grew. The imperial crown changed heads no fewer than seven times in the span of two decades – known as the Twenty Years’ Anarchy. Only with Leo’s usurpation of the throne from its former occupant, an accountant named Theodosios III (himself a usurper installed by one faction of the army), did the purple of imperial office come to rest on the same shoulders for a while. And not a moment too soon, as far as the empire was concerned; the Arab host appeared before the walls of Constantinople less than five months after Leo’s coronation.

The year before he took the throne, when still Strategos of the Anatolikon Theme and the empire’s most powerful general, Leo had deceived the Arab General Maslama in a secret meeting somewhere near the city of Amorium in central Anatolia. Leo somehow convinced Maslama that, if the Arab withdrew his troops south from Amorium for a while, this would enable Leo to march unchallenged on Constantinople and take the throne as emperor, on the understanding that he would then meekly submit to the sovereignty of the Caliph Sulayman. Of course, Leo had no intention of honouring this agreement. Once he had taken the throne, he set about preparing the city’s defence. In spite of this it seems that Maslama was remarkably reluctant to acknowledge that he had been tricked. Leo’s boast that, were Maslama a woman he would do whatever Leo wanted, comes – perhaps tellingly – from an Arab source recounting the events of the siege.

All the historians I have read of this period are agreed: had Constantinople fallen, there would have been little to stop the Umayyad dynasty swallowing up the rest of Europe in their ever-burgeoning empire. The acquisition of an asset as valuable and strategic as Constantinople would likely have strengthened the Umayyad Caliphs beyond challenge. As it was, their eventual downfall came from within.

The events of the siege itself are much as I described. The Arab land forces arrived on 15 August AD 716 to the west of the city. The Arab fleet arrived two weeks later on 1 September. However, the land walls and the so-called ‘Greek fire’ proved insurmountable obstacles to their success.