Battle of Heliopolis The Battle of Heliopolis , or " Ayn Shams , " was a decisive battle between Arab Muslim armies and Byzantine forces for the control of Egypt . Though there were several major skirmishes after this battle , it effectively decided the fate of the Byzantine rule in Egypt , and opened the door for the Muslim conquest of the Byzantine Exarchate of Africa . Background to the Islamic conquests . At the time of the death of Muhammad on 6 July 632 , Islam had effectively unified the entire Arabian peninsula . Within the next twelve years , under the rule of the first two Caliphs an Islamic empire arose that annexed all of what used to be the Sassanid Empire , and most of the eastern provinces of the Byzantine Empire . The Muslim Caliphate continued to expand until by the turn of the 8th - century , it stretched from the Atlantic Ocean in the west to Central Asia in the east . Under the first Caliph , Abu Bakr , force was used to prevent unrest and rebellion from causing the collapse of the new Islamic state , and the first raids were carried out into the territory of the Sassanid Empire . But the all out attack on the neighboring empires came with the ascension of the second Caliph , Umar . When the new Caliph began his rule in 634 , the international situation in the Middle East could hardly have been more propitious for a new and ambitious power : the region ' s two traditional main powers , the Byzantine and the Sassanid Empires , had exhausted each other in a conflict that raged for over 20 years . By the 630s , Sassanid Persia had descended into a state of civil war , while Byzantium , under the aging emperor Heraclius , its manpower and resources depleted in the struggle with its old adversary , was struggling to re - establish its authority in its newly re - conquered eastern provinces . The two states were thus in considerable internal turmoil , and unable to either stop the Muslim expansion or to recover from its first blows . It is unknown whether Umar intended from the outset to conquer both the Sassanid and the Byzantine Empire , or simply allowed raids , and then , perceiving their weakness , followed up with full - scale invasion . Arab invasion of Egypt . After successfully conquering Syria between 634 and 638 , the Arabs turned their attention to Egypt . The attack on Africa took the Byzantines by surprise . Heraclius ’ s generals had advised him that the Muslims would need a generation to digest Persia before undertaking another wholesale invasion . The increasingly frail Emperor was forced to depend on his generals , and the result was complete disaster . In 639 , less than a year after the complete fall of the Sassanid Empire , an army of some 4 , 000 commanded by Amr ibn al - A ' as , under orders of Omar , began the invasion of the Diocese of Egypt . That relatively tiny force marched from Syria through El - Arish , easily took Farama , and from there proceeded to Bilbeis , where they were delayed for a month . But having captured Bilbeis , the Arabs moved again , eerily echoing Heraclius ’ successful campaign against the Sassanids just a short decade ago . A small force , commanded by a charismatic and tactically brilliant commander went behind enemy lines , and caused chaos all out of proportion to their size . They laid siege to Babylon , which after a small effort at negotiation , was taken by storm on 6 April 640 , which was Good Friday . Having finished there , Amr rode on . He and his army marched ( or rode ) to a point on the Nile called Umm Dunein . The siege of this city caused Amr and his horsemen considerable difficulty as they lacked siege engines and overwhelming numbers . After finally taking Umm Dunein , Amr crossed the Nile to Faiyum . There , on 6 June 640 , a second army dispatched by Omar arrived at Heliopolis and began to lay siege to it . Amr retraced his route across the Nile River , and united his forces with those of the second army . They began to prepare for movement towards Alexandria – but scouts reported the approach of the Byzantine army . The battle . At that point the united Arab army was confronted by a Roman army , which Amr , who had taken overall command , defeated at the Battle of Heliopolis . Just as Byzantine generals had failed utterly in Syria , they failed equally spectacularly in Egypt , and the Empire ' s economically most valuable province after Anatolia was lost . The battle took place sometime in early to mid July 640 , near the ancient city of Heliopolis , with Arab forces totaling approximately 15 , 000 under the command of Amr ibn al - A ' as , and the Byzantine forces estimated at well over 20 , 000 under Theodore , commander of all Byzantine forces in Egypt . The Byzantine army could have responded sooner , but had not , for reasons that will never be known . Though historians such as Butler blame the treachery of the Coptic Christians as well as the failure of the Byzantine generals for the swift fall of the Exarchate of Egypt , Gibbon does not blame anyone as much as he praises the character and genius of Amr for the victory at Heliopolis . Gibbon says " the conquest of Egypt may be explained by the character of the victorious Saracen , one of the first of his nation . " Whether through the foolishness of the Byzantine generals , including Theodore , contributed to what then occurred , certainly Amr fought a brilliant battle at Heliopolis . When the Byzantine army began approaching , Amr divided his army into three separate units , with one detachment under the command of a trusted commander , Kharija . This unit marched abruptly east to near - by hills , where they effectively hid . This unit was to remain there until the Romans had begun the battle , at which point they were to fall on the Roman flank or rear , whichever was more vulnerable . The second detachment Amr ordered to the south , which would be the direction the Romans would flee if the battle went badly . Once the Byzantine forces initiated contact with Amr ' s forces and commenced an attack , the detachment of Kharija attacked the Byzantine rear , which was completely unexpected by the Romans Theodore had not kept scouts out , or , if he had , he ignored their warning of the approaching Arab horsemen . This attack from the rear created utter chaos among the Byzantine ranks . As Theodore ' s troops attempted to flee to the south , they were attacked by the third detachment , which had been placed there for just such a purpose . This completed the final break - down and defeat of the Byzantine army , which fled in all directions . Theodore survived , but with only a tiny fragment of his army , while the remainder was killed or captured . In the battle ' s aftermath , most of southern and central Egypt fell to Amr ' s forces . The defeat at Heliopolis was crucial , as it removed the last Roman force standing between the Islamic invaders and the heart of Egypt . However , not only did the Battle of Heliopolis leave Egypt practically defenceless , it also encouraged the disaffected natives , most of whom were Monophysite Christians and had suffered on - and - off persecution at the hands of Constantinople , to rise up against their Roman oppressors . Although the Byzantine Empire was certainly by lineage the Roman Empire , its traditions , language , and ruling elite , by this time , were Greek . The Greeks of Egypt , whose numbers could scarcely equal a tenth of the native population , were overwhelmed by the universal defection of those same natives from obedience to the Roman Empire . As Bury wrote in the " History of the Later Roman Empire from Arcadius to Irene " : The native population had heard that taxation and rule under the Caliphate was far better than that of the Romans , and once the Battle of Heliopolis left the Romans without an army to force their obedience , that obedience was gone , and a large portion of the Coptic Christians sided with the invading Muslims over the Byzantines . Ironically , some Copts believed they would find the Muslims more tolerant than the Byzantines , and of these some turned to Islam . In return for a tribute of money and food for the troops of occupation , the Christian inhabitants of Egypt were excused military service and left free in the observance of their religion and the administration of their affairs , while Amr was Emir of Egypt . A smaller number sided with the Byzantines , hoping that they would provide a defense against the Arab invaders . It is notable that after the end of Amr ' s rule in Egypt , the population found their taxes ever increasing . Indeed , under the Umayyad Caliphate the Coptic Christians of Egypt found their taxes higher than the Byzantine Greeks had ever made them . Aftermath . The next year and a half were spent on more maneuvers , skirmishes , and sieges before the formal surrender of the capital , Alexandria , took place on 4 November 641 , but Sir Walter Scott was correct when he said “ the fate of Byzantine Africa was decided at the Battle of Heliopolis . ” The permanent loss of the Egypt left the Byzantine Empire without an irreplaceable source of food and money . The loss of Egypt and Syria , followed later by the conquest of the Exarchate of Africa also meant that the Mediterranean , long a " Roman lake " , was now contested between two powers : the Muslim Caliphate and the Byzantines . In the event , the Byzantine Empire , although sorely tested , would be able to hold on to Anatolia , while the mighty walls of Constantinople would save it , during two great Arab sieges , from the fate of the Persian Empire .