<P> The siege's failure had wide - ranging repercussions . The rescue of Constantinople ensured the continued survival of Byzantium, while the Caliphate's strategic outlook was altered: although regular attacks on Byzantine territories continued, the goal of outright conquest was abandoned . Historians consider the siege to be one of history's most important battles, as its failure postponed the Muslim advance into Southeastern Europe for centuries . </P> <P> Following the first Arab siege of Constantinople (674--678), the Arabs and Byzantines experienced a period of peace . After 680, the Umayyad Caliphate was in the throes of the Second Muslim Civil War and the consequent Byzantine ascendancy in the East enabled the emperors to extract huge amounts of tribute from the Umayyad government in Damascus . In 692, as the Umayyads emerged as victors from the Muslim Civil War, Emperor Justinian II (r . 685--695 and 705--711) re-opened hostilities . The result was a series of Arab victories that led to the loss of Byzantine control over Armenia and the Caucasian principalities, and a gradual encroachment upon Byzantine borderlands . Year by year, the Caliphate's generals, usually members of the Umayyad family, launched raids into Byzantine territory and captured fortresses and towns . After 712, the Byzantine defensive system began to show signs of collapse: Arab raids penetrated further and further into Asia Minor, border fortresses were repeatedly attacked and sacked, and references to Byzantine reaction in the sources become more and more scarce . In this, the Arabs were aided by the prolonged period of internal instability that followed the first deposition of Justinian II in 695, in which the Byzantine throne changed hands seven times in violent coups . In the words of the Byzantinist Warren Treadgold, "the Arab attacks would in any case have intensified after the end of their own civil war...With far more men, land and wealth than Byzantium, the Arabs had begun to concentrate all their strength against it . Now they threatened to extinguish the empire entirely by capturing its capital ." </P> <P> The information available on the siege comes from sources composed in later dates, which are often mutually contradictory . The main Byzantine source is the extensive and detailed account of the Chronicle of Theophanes the Confessor (760--817) and secondarily the brief account in the Breviarium of Patriarch Nikephoros I of Constantinople (died 828), which shows small differences, mainly chronological, from Theophanes's version . For the events of the siege, both authors appear to have used a primary account composed during the reign of Leo III the Isaurian (r . 717--741) which therefore contains a favourable depiction of the latter, while Theophanes apparently relies on an unknown biography of Leo (ignored by Nikephoros) for the events of 716 . The eighth century chronicler Theophilus of Edessa records the years leading up to the siege and the siege itself in some detail, paying particular attention to the diplomacy between Maslama and Leo III . The Arab sources, mainly the 11th - century Kitab al -' Uyun and the more concise narrative in the History of the Prophets and Kings by al - Tabari (838--923), rely on primary accounts by early 9th - century Arab writers, but are more confused and contain several legendary elements . The Syriac language accounts are based on Agapius of Hierapolis (died 942), who likely drew from the same primary source as Theophanes, but are far briefer . </P> <P> The Arab successes opened the way for a second assault on Constantinople, an undertaking already initiated under Caliph al - Walid I (r . 705--715). Following his death, his brother and successor Sulayman (r . 715--717) took up the project with increased vigour, according to Arab accounts because of a prophecy that a Caliph bearing the name of a prophet would capture Constantinople; Sulayman (Solomon) was the only member of the Umayyad family to bear such a name . According to Syriac sources, the new Caliph swore "to not stop fighting against Constantinople before having exhausted the country of the Arabs or to have taken the city". The Umayyad forces began assembling at the plain of Dabiq north of Aleppo, under the direct supervision of the Caliph . As Sulayman was too sick to campaign himself, however, he entrusted command to his brother Maslama ibn Abd al - Malik . The operation against Constantinople came at a time when the Umayyad state was undergoing a period of continuous expansion to the east and west . Muslim armies advanced into Transoxiana, India and the Visigothic Kingdom of Hispania . </P>

Who were the leaders of the two opposing armies during the last siege of constantinople