Conquests during Umar’s Caliphate
By: Rasul Ja'fariyan
Continued Conquests in Damascus and Egypt
After conquering Damascus, the consecutive victories of Muslim Arabs forced many cities to ask for peace beforehand as they could gain more concessions. The city of Ba'labakk was peacefully conquered in the year 15th A.H. In the month of Rabi' al-Thani of the same year, the city of Hims which was considered one of the biggest cities of Damascus, was invaded by Muslims.
According to Baladhuri, the people of Hims who witnessed the escape of Heraclitos from their city and were aware of the repeated victories of Muslims and their patience and perseverance, took refuge inside the city after a brief encounter outside the town and called for mercy from Muslims.
In the peace deal concluded, in addition to guarantees for their life and properties, it was agreed that the city wall and churches would remain intact. Only a quarter of the Johannes church was excluded for the construction of a mosque. Muslims, too, settled down in deserted areas and in houses abandoned by their owners. 
At that time, Abu 'Ubayda divided the governorship of different regions among army commanders. Yazid Abi Sufyan was chosen for ruling Damascus, Shurahbil Ibn Hasana for Jordan, 'Amr Ibn 'As for Palestine and 'Ubayda Ibn Samit for Hims. Abu 'Ubayda, himself, set off towards Humat and Shayzar for expanding the conquests.
Heraclitos who had now lost key centers in Damascus, once again tried to organize a huge army of Romans, Damascus people, the people of Hijaz and Armenians besides the Arab tribes of Judham, Lakhm and others to fight Muslims. In historical sources, these tribes have been named as “al-Musta'raba”. 
This big war took place at the Yarmuk region which was the name of a river. Muslims are said to have numbered at 24000 and the Roman army and its allies at 200000. But, one should not forget that Heraclitos did a last-ditch effort to keep Damascus. This war was so tough for Muslims that even Muslim women had to fight. 
The Yarmuk battle ended in Muslims' victory and following his defeat, Heraclitos left for Constantinople. In this war, Jabala Ibn 'Ayham commanded the front line army of Rome. There are different stories in various sources about whether he had converted to Islam or not, why he had taken offense from 'Umar and why 'Umar had repented from his treatment of him. 
One year after the Yarmuk battle, Muslims succeeded in surrounding Bayt al-Muqaddas. Abu 'Ubayda first invited them to either accept Islam or pay Jaziyya (poll tax paid in lieu of conversion to Islam).
However, when they refused, they had to lay a siege on the city. The Nazarene community of the city, who found the situation critical, gave in to a compromise, provided that the caliph would come to al-Quds and sign the contract personally. 
'Umar was doubtful about going to Quds. So, he consulted some of the Companions. 'Uthman was opposed to the idea, but in the presence of Imam 'Ali (a), he encouraged 'Umar to go, saying it was to the benefit of Islam and Muslims. 'Umar accepted his idea. After appointing 'Uthman as his vicegerent in Medina, he headed for Quds.  He moved towards Damascus arguably in the year 16th or 17th A.H. 
A variety of agreements were mentioned in the peace accord 'Umar signed with Damascus's Nazarene community. They received assurances that their lives would be spared. They were also assured that no church would be damaged nor any swastika broken. One of the key conditions of the accord was that Muslims should not allow Jews to live in Quds, nor should there any obligation in faith.
The residents of al-Quds also pledged to pay toll like the people of Ctesiphon. Additionally, the Romans had to leave the city. The people were also free to move their belongings to Rome or anywhere else.  It was on this trip that 'Umar entered the mosque and inquired Ka'b al-Ahbar about the site of the altar.
“The altar should be built towards the cliff which used to be the Qibla of Jews,” Ka'b said..
'Umar was infuriated at the response, saying, “Your response resembles the words of Jews.” 
Some time after the return of 'Umar from Damascus, a dreadful epidemic of plague dubbed ”'Amwas” swept Damascus in 18 A.H. The plague claimed the lives of several Muslims including the top governor of Damascus.
Chief among the victims were Abu 'Ubayda Ibn Jarrah, Mu'adh Ibn Jabal, Yazid Ibn Abi Sufyan, Shurahbil Ibn Hasana, Faďl Ibn 'Abbas and Suhayl Ibn 'Amr. Yazid died a few while after Abu 'Ubayda as he had replaced him. After his death, 'Umar appointed Mu'awiya. Abu Sufyan, who had lost his eyesight at that time, appreciated 'Umar for visiting him.  In the last few years of 'Umar's caliphate, Mu'awiya was the governor of the Greater Syria. 
One of the key towns conquered in the reign of Mu'awiya was Caesarea. It was arguably conquered in 18 or 19 A.H.  The Arab troops were conquering further territories in the Greater Syria. In the meantime, the small towns accepted the peace treaty on their own. Many Arabs and Nazarenes adopted Islam. 
When 'Umar was in Damascus, 'Amr Ibn 'As asked for his permission to expedite towards Egypt to conquer it. It is said that in the Dark Age, he had gone to Egypt for business. So, he was somewhat familiar with it. 
'Umar was afraid of launching such a bid. As a result of 'Amr's insistence and his efforts in playing down the risk of the attack, he eventually gave in. Amro, headed by a troop of between 3500 to 4000 men, headed for Egypt. It has been narrated that after the expedition of 'Amr, 'Umar withdrew his support and told 'Amr that if he had not yet entered Egypt, eh should return. However, 'Amr had entered Egypt. It seems 'Uthman had accused 'Amr of expansionism, and had magnified the danger of the elimination of Arab troops before 'Umar. 
Egypt's governor whom Arabs called “Muqawqis” had been appointed by Romans to rule the country. He was Coptic. Hence, Prophet Muhammad (S), in a letter to him, had called him the “Chief Coptic”. The war between Muslims and the Muqawqis army lasted two years. In the meantime, Muslims conquered many areas and towns.
The main reason behind the conquest of Egypt was the difference between Egyptian Coptics and Romans. The Coptics were not very willing to defend the Romans. Muqawqis, himself, was doubtful over this matter and waited to see what would happen. His brother, Benjamin, was the bishop of Alexandria.
In the meantime, Cyrus, the envoy of the Roman emperor, had arrived in Egypt to reform the affairs. The stringent behavior further distanced the Coptics from the Romans.  The news of the consecutive conquests of the Arab troops in the Greater Syria encouraged further people to surrender. 
The prolonged conquest of Alexandria, which dragged on for four months, necessitated the dispatch of auxiliary forces to Egypt.  The town eventually fell to Muslims in 20 A.H. There is debate as to whether Egypt gave in through force or peace. The same doubt exists for many other towns. After the deployment of Muslims, they turned the town of Fustat, which was their military base, to their administration center and left Alexandria. This was interesting from political and militarily viewpoints.
Among the troops of 'Amr Ibn 'As, there were some non-Arab fighters, some of whom were ethnic Romans and were called “Hamra'”. The other group was the Yemeni-based Persians who had moved, along with the Arab tribes, to these regions. Following the conquest of Egypt, the Iranians were accommodated in a certain place. According to Ibn 'Abd al-Hakam, the mosque raised by Muslims at the site was famous until his age in the 3rd century A.H. 
A variety of matters have been mentioned over the reasons for the escalation of Arab conquests. The conquest of every region had certain reasons. The conquest of Iran, for instance, had a totally different reason from that of Damascus. These conquests were entirely achieved by Arab Muslims.
So, it is evident that their will was the first reason for these conquests. This will stemmed, on the one hand, from their faith, and on the other from their leadership and the Muslims' administrative and legal systems over war booties.
Islam allocated a large portion for the warriors and it was natural for the needy and the hungry Arabs to go the battlefield to earn something for their families, provided that they would emerge alive from the battlefield. As a matter of fact, Muslims had no concern whatsoever of being killed, because they saw martyrdom in the path of Allah as a great achievement.
The staggering point about their will and determination was that Muslims had a high sense of self-confidence. Prophet Muhammad (S) promised Muslims victory over the Roman Empire and Iran saying, “The treasures of Caesar and Chosroe will fall to you”. Therefore, Muslims moved towards the battlefield with an iron will and full confidence in the forecast of the Prophet. Initial gains made them stronger, livelier and more confident for later conquests.
Another point is that the power of Muslims did no depend on a particular caliph, because a survey of these conquests from their start to the end of the first century A.H indicates that every caliph who had the chance of conquest, managed to capture several lands. The people's belief in the administration was a driving force of these conquests.
No opposition was raised from the side of Medina rulers. The rulers under the caliph were totally obedient. It should be noted that the caliphs picked their appointees from among the people of the second generation of the Companions who were totally submissive to them. Yet, the significance of the conquests crated an atmosphere in which even potential opponents abandoned their dream of a political rebellion. Under these circumstances, the masses of troops pressed ahead with their conquests more comfortably.
The success of Arabs in Damascus had several reasons, one of which was that the majority of the Damascus residents were Arabs, and in spite of being Christians, they were racially linked to Hijaz. Meantime, they maintained their distance from the Romans. In the early years of the conquests, some tribes including Lakhm and Judham joined Muslims, but when they found out that the war was serious, they fled to the nearby villages and left the Muslims alone. 
According to Jabala Ibn 'Ayham, the relationship of the Ansar, who originally came from the southern tribes, to him was, ÃäÊã ÇÎæÊäÇ æÈäæ ÃÈíäÇ “You are our brethren and children of our fathers.”
During the conquest of Qinnasrin, the residents of the town hinted that they were also Arabs and did not want to fight against the conquerors. So, Khalid accepted their peace overture.  The Taghlab tribe, who had teamed up with the Romans and fought along with them, said in the 13th century A.H that they would fight along with their tribe.  There were, however, a number of other tribes who remained allied with the Romans till the end, and immigrated to the Roman territories after the conquest of the Greater Syria by Muslims.
Apart from the Arab residents of Damascus disassociated themselves from the Romans, others including Jews, the Nibti community and the Egyptian Coptics, had the same situation. Faced with the mild dealing of Muslims, they felt they could live up with Muslims and see their rights met. As soon as Muslims captured Hims, they found themselves involved elsewhere in the Yarmuk war.
They believed that they might not emerge victorious out of the Yarmuk battle, they decided to return the money received from the people of Hims to provide for their security. Faced with such a conduct, the people of Hims said, “Your friendship and justice is more likeable to us than the oppression which we are living under. We will defend our town along with you.” 
It has been said that the Nibtis aggressively cooperated with Muslims, and as the Romans did not suspect them, they spied for Muslims. 
The other point is that the there were religious differences between Damascus and Rome. Considering the fact that the Romans did not treat these people properly from both economic and political viewpoints, the remarks of Will Durant hold true, “As the conqueror Arabs invaded Egypt and the Far East, half the people of those regions welcomed their arrival, because they viewed them as their liberator from the clutches of religious, political and economic oppression of the Byzantine capital.”  At any rate, after the expansion of conquests, several towns followed the line of surrender. 
Continued Conquests in Iraq and the Conquest of Iran
'Umar's caliphate was accompanied with several conquests of Muslim troops in Syria, which started with the conquest of Damascus. In these circumstances, some measures had to be adopted in Iraq. Firstly they were needed to stabilize its situation in favor of Muslims and, secondly, to expand the conquests. In the meantime, the town of Hira was freed from the Iranian control. Hence, Iranians were waiting for an opportunity to repel the new threat.
Arab troops were led by Muthanna Ibn Haritha. Yet, Medina's caliph, like the era of Abu Bakr, was determined to dispatch a commander from the known Saudi clans to Iraq. The nominee was Abu 'Ubayd Ibn Mas'ud Thaqafi, the father of Mukhtar, from the Thaqafi clan, which used to be an ally of the Quraysh. Heading a 5000-strong troop , Abu 'Ubayd encouraged many tribes on his way to conduct Jihad and win booties.
A large number of people joined him.  It was decided that Muthanna work under the command of Abu 'Ubayd. Iranians amassed a troop headed by Bahman Jadiwayh (Men of Shah Hajib) east of the Euphrates, whereas Abu 'Ubayd's forces lined up on the western side of the Euphrates. The Arabs crossed the bridge and launched the battle.
Despite the bravery of Muslims, the mammoth elephants existing in the Iranian army frightened the horses of Arab forces. As the Arabs had damaged the bridge, they had no way back. So, they sustained heavy losses and casualties. At any rate, a temporary bridge was built over the river and the Arabs lost out the war to Iran which was dubbed “Yawm al-Jisr” or the Day of the Bridge with a death toll of 4000 people. 
Ibn A'tham, however, has narrated this event in a manner that it seems Muslims could defeat the Iranians and return to their army base.  Yet, the fact that the Iranians did not chase the Muslims indicates that they lacked the necessary readiness to do so. This even probably occurred in Sha'ban or Ramaďan 13 A.H. 
Abu Mikhnaf and others say 'Umar was upset even until one year after the Jisr event. In the meantime, Muthanna Ibn Haritha called the Arabs to Jihad. 'Umar gradually thought of continuing the operation. Afterwards, around 700 people headed by Mikhnaf Ibn Salim, thousands headed by 'Adi Ibn Hatim, and a number of people from the Banu Tamim tribe joined the Arab troops in Iraq.  The Bujayla tribe also joined the Arab force, under the condition that one-fourth of the booties would be given to them. 
The Arabs clashed with the 12000-strong Iranian troops, headed by Mihran Ibn Mihrbandad (Mihrwayh Hamadani)  at the Buwayb, a river branching out from the Euphrates River. Mihran was killed in the battle and the Iranian army suffered a crushing defeat. Several Iranians were captured and Muslims earned large amounts of booties.
Muthanna displayed noticeable bravery in the battle. The poems of 'Urwa Ibn Zayd al-khayl about the command of Muthanna are notably exaggerating, “Among the commanders of Iraq, we have not seen anybody like Muthanna who belongs to ash-Shayban.”  Some time after the event, Muthanna Ibn Haritha died from the wounds he had sustained in the Jisr battle.
The battle occurred arguably in the 13th or 14th A.H. As 'Umar did not take any action for battle until a year later, this event should have not taken place sooner than 14 A.H. The victory boosted the morale and courage of Muslims and they constantly invaded the Iraqi lands which were still under the control of the Iranians. They also invaded a large market place set up near Baghdad. This issue indicated that Iran was not capable of providing the security of Iraq and had to think of a solution as soon as possible.
According to Dinwari, when Suwayd Ibn Qutba (who had some power around Basra) heard the news of these wars from Muthanna Ibn Haritha, he demanded 'Umar to strengthen the weak situation of southern Iraq and dispatch some forces to the region. 'Umar who seemingly did not have much trust in Suwayd to transfer the military command to him, sent a contingent of 1000 people, headed by 'Utba Ibn Ghazwan, to the region. 'Umar accompanied 'Utba out of Medina.
Referring to the passage of Muslims forces from the Euphrates through Hira to Ctesiphon, he told him to move towards Ahwaz and dissuade its residents from helping the Iranian army. 'Utba reached the place nowadays called Basra where there were only a number of ruined houses. It was the residence of Iranian border guards, who were commissioned with preventing the aggression of Bedouin Arabs.
The first region attacked was Ubulla, on the outskirts of Baghdad. 'Utba wrote the news of this victory to the caliph, describing the town as a harbor of ships coming from 'Umman, Bahrayn, Fars, India and China.  When the news of the victory reached Medina, the people asked 'Utba's envoy about the situation of the region. He told them about the amounts of gold and silver which Muslims had obtained. The news triggered an influx of Arabs towards the region. 
Ubulla was located four leagues from Basra. It apparently existed until the 7th century A.H.  With the development of Basra, Ubulla lost its grandeur. Ubulla and other towns like Khurayba which was conquered shortly later, were said to be the concentration center of Iranian border guards.
Yaqut says, “Basra was built beside an ancient Iranian city named Vahishtabad Ardishir. This city was ruined in the attacks of Muthanna Ibn Haritha, so when Muslims went to that region to build Basra, they called the city “Khurayba” (ruin).  Afterwards, Khurayba became a district of Basra.
According to Dinwari, the conquest and establishment of Basra took place before the Qadisiyya war. The fact that Basra was constructed before Kufa indicates that 'Utba had reached southern Iraq before reaching Qadisiyya. Noting this issue, Yaqut has mentioned that after reaching Qadisiyya, 'Utba moved to southern Iraq and to Basra. 
What is important is that around 15 and 16 A.H, two war fronts were opened against Iran, one in Kufa where some troops were advancing towards Ctesiphon, and the other in Basra from where the Arabs were moving to capture the southern Iranian lands in Khuzistan.
The two fronts led to the establishment of the two important towns of Basra and Kufa in Iraq, which later laid the cornerstone of the Islamic Iraq, in addition to Baghdad which was built in the 2nd century A.H. It is said Basra refers to a land which has black pebbles.  Quoting Hamza Isfahani, Yaqut says that according to Mubadh Ibn Asawhasht, Basra is the Arabic form of “Bas Rah”, meaning so many roads, because several routed led to this town. 
After the conquest of Ubulla, 'Utba Ibn Ghazwan asked the caliph to set up a town for Arab immigrants. After studying the regional situation, 'Umar authorized the construction of the town. Thus, Basra was founded. After a while, 'Utba felt that Sa'd Ibn Abi Waqqas was exceeding his limits in giving him unrelated orders. 'Utba, who considered himself an appointee of 'Umar, protested to Sa'd and left for Medina.
As soon as 'Umar heard the news, he asked, “Why is he not ready to accept the rule of a man from the Quraysh who has been a Sahabi, too?” 'Utba protested that he, too, was a ruler from the Quraysh and that Prophet Muhammad (S) had said, ãæáì ÇáÞæã ãäåã “Lord of people is from Ahl al-Bayt.”
It seems that 'Umar had asked 'Utba him to return to Basra, but 'Utba died shortly. 
In an address to the people of Basra, 'Utba said in 17 A.H that, Åäå áã Êßä ÇáäÈæÉ ÅáÇ ÊäÇÓÎåÇ ãõáß¡ ÝÃÚæÐ ÈÇááå Ãä íõÏÑßäÇ Ðáß ÇáÒãÇä ÇáÐí íßæä Ýíå ÇáÓáØÇä ãõáßÇð “There is no prophethood not to have been rejected by a king. I seek refuge in that the Allah from the day Sultan becomes the king.” 
We said that the Buwayb event frightened the Iranians. This time, the Iranians mobilized a larger army led by Rustam Farrukhzad—the commander of Iranian forces in Adharbayjan—to prevent Arabs' invasion. Ibn A'tham has described the way Bahram, the governor of Hamadan; Shirzad, the governor of Qum and Kashan; Banduwan, the provincial governor of Isfahan and Khurshid, the governor of Riy, dispatched their forces to the battlefield. 
In return, the caliph had to find a powerful commander for his troops. 'Umar initially thought he would travel to Iraq, but the Medina notables advised him against it. A number of people were nominated for the command, one of them Imam 'Ali (a). Advised by 'Umar, 'Uthman talked with Imam 'Ali (a). Yet, Imam shunned accepting the responsibility. The next choice was Sa'd Ibn Abi Waqqas who was suffering from a thigh injury. 
He could not even mount on the horseback.  So, he did not attend the battle. The battle ever marked the worst defeat of the Iranians was called the “Qadisiyya war”. Qadisiyya was the name of a small border town located amid the Taff Desert, 50 miles from Kufa. The town had a fortress and some palm groves and plantations. Around 4-6 miles from Qadisiyya, there was a resort named 'Udhayb which had a spring, and was virtually the end of the desert. Sa'd set up his camp at 'Udhayb, whereas Rustam camped outside Qadisiyya. 
Wild conjectures have been given over the number of Iranian and Arab forces. Yet, it can be guessed that the Arab forces numbered between 20 to 30 thousand  and the Iranians were between 3 to 4 thousand more. Meanwhile, Ibn A'tham has put the number of Arab forces at 60 thousand.56 Rustam remained at Diyr A'war  for four months to settle the matter peacefully. Rustam tried to satisfy the Arabs, whom he thought, were fighting for food. 
Additionally, the four months of stay at the camp could weaken the power of Arab forces. On the other hand, Muslims did not abandon their condition that the Iranians should accept Islam and pay toll or engage in war. Acceptance of the first two proposals of the Arabs was impossible, because Iran was a superpower. So, Rustam had to give in to war.
Ibn A'tham writes, “At the request of Yazdgard, Sa'd sent some envoys including Mughira h to Ctesiphon to Yazdgard's court. As they entered the court, they sat on the ground except Mughira h who sat by the king on his seat.
The king asked him, “What are these clothes? What are you wearing?”
Mughirah replied, “It is Yemeni silk.”
Yazdgard took this as bad omen and said in Persian, “Burdand Jahan ra,” meaning “They plundered the world”.  So, he ordered the start of the war. The Qadisiyya battle lasted only four days, with each day having a specific name. They were called Armath, Aghwath, 'Ammas and Qadisiyya.  The battle ended in favor of Arabs and Rustam was killed during the war. The Iranian forces withdrew as far as Diyr Ka'b where new forces under the command of Nukharijan helped them.
Therefore, the Iranians refurbished their army and made a new onslaught. Dinwari says as Nukharijan entered the battlefield, he began crying out “any man, any man” to invite a contender.  Nukharijan was, however, killed by Zuhayr Ibn Sulaym (Mikhnaf Ibn Sulaym's brother). This time, too, the Iranians were defeated and withdrew as far as Ctesiphon.
The Arabs achieved the win very hard, because they suffered huge losses. It is said that a group of Iranians gathered around Iran's black flag, saying, “We will not abandon our place unless we are killed.” and they did so.  The bravery of the Iranians made it difficult for the Arabs to defeat them. Abu Raja' Farsi quoted his grandfather, who had been in the Iranian army at the Qadisiyya war, as saying that the Arabs had to spray many arrows on the Iranians and the battle had become so tough for them. 
There are differences of opinion on the year of this war. Waqidi has conceded that it took place in 16 A.H.  Armenian historian, Ilyas Nusaybini, has cited Jumadi al-Awwal 16 A.H as the date of the war. Meanwhile, Ibn Ishaq has mentioned 15 A.H as the year of the war.57 A researcher has said that the war occurred in the month of Sha'ban, 15 A.H.  During the war, the emblem of the Sassanids troops fell to Muslims;  an issue which indicates the crushing blow that the Iranian government suffered in the war.
In the aftermath of the war, Sa'd found out the necessity for establishing a town named “Dar al-Hijra” for the tribes who had immigrated to the region from Hijaz for war. Had Basra been established by then, it could have been a model for Kufa. Yaqut has cited ten reasons for the naming of Kufa. 
It is said that a number of places were surveyed. As the site was suitable for the raising of sheep, horses and camels, 'Umar preferred Kufa , which was previously called Surastan.  After the site of the mosque and the palace of administration were determined, the nearby regions were divided between the northern and southern tribes.
The town initially seemed transient because the tribes set up their houses from reed. So, at times of Jihad, they removed the reed framework and ceded them to others. As they took their wives with themselves to the war, they had to build new quarters after their return. It was only at the time of Mughira that people began to build clay structures. Yet, they did not build any rooms inside. Under the reign of Ziyad Ibn Abih, brick houses became popular.
Yaqut writes that the caliph wrote to Sa'd, saying the mosque should have enough space to accommodate the participants in the war. So, it was built with a capacity of 40 thousand people. 
Hence, Kufa became one of the most important Islamic towns. At the same time, 'Umar sent a letter to the people of Kufa, writing, “To the people of Kufa, to the center of Islam.” He also said of Kufa that it was, Åáì Ãåá ÇáßæÝÉ¡ Åáì ÑÃÓ ÇáÅÓáÇã “To Kufiyans, to center of Islam.” And saying about that, åã ÑãÍ Çááå æßäÜÒ ÇáÅíãÇä æÌãÌãÉ ÇáÚÑÈ “They are divine spear, treasure of faith and renowned among Arabs.”
Salman has also called Kufa as the place “where there is Islam”. 
After the Qadisiyya war, Muslims chased the Iranians and set up a military camp on the western rim of the Euphrates n front of Ctesiphon. According to Dinwari, they stayed there for 28 months, so long that they could eat dates of the palm trees twice!  By that time, Muslims had dominated parts of Ctesiphon or Ctesiphon—meaning towns in Arabic.
Ctesiphon consisted of seven nearby towns, protected by barracks. Entry into the greater town was possible through symmetrical gates designed around the city. On the Western side of the Tigris, were the cities of Bih Ardishir (Arabic, Bihrasir), Seleucids (Sulukiyya), Darzijan, Sabat and Mahuza while on the river's eastern side were the cities of Ctesiphon, Asbanbar and Rumiyya which was called Wiya Andyu Khusraw. The king resided at Ctesiphon's white palace and the palace of Mada'in where the banquets and parties were held, was located in Asbanbar. 
Muslims captured the Western area after a brief clash and were stationed in Bihrasir. The destruction of bridges by Iranians  kept Arabs behind the Tigris for a long time but they finally managed to cross the river and enter the town. When Iranians saw the Arabs, they cried out, “The devils came! The devils came!” 
Kharihzad was initially supposed to stay in Mada'in as long as possible. However, when Arab crossed the Tigris and reached behind the city gates, fled from the town's eastern side and retreated towards western Iran.  The Arab's entry into the city was as a big victory for them. Now, the capital of the Sassanids kingdom had been conquered and numerous booties were available to Arabs. Among them, were things Arab had never seen until then. For instance, they poured camphor into their food, thinking it was salt! 
Before that, Yazdgard had taken the royal family along with the treasures and other portable belongings and had fled to Qasr Shirin  in Iran's western mountains. From there, he went to the town of Hulwan near the present-day town of Sar Pul Dhahab. Kharihzad, too, who had failed to keep Ctesiphon, set off in the same direction and settled in Jalula.
In order to keep Ctesiphon, Arabs had no way but to chase this army. Therefore, Sa'd Ibn Abi Waqqas sent an army led by Hashim Ibn 'Utba to follow them. Iranians dug a ditch around them in Jalula, waiting for the arrival of backup forces from Yazdgard, Jibal and Isfahan. But, Muslims did not wait for these forces and launched the offensive.
In this battle, Hujr Ibn 'Adi commanded the left wing of the army of Islam. Iranian forces were defeated in the war and had to retreat to Hulwan. After that, Yazdgard did not see it right to stay any longer in Hulwan, so he fled towards the region of Jibal in Qum and Kashan. A 4000-strong force of Muslim Arabs was tasked with protecting Iraq against the infiltration of Iranians in Jalula.  Now, Muslims were on the eastern side of the Tigris as well and were conquering those regions. Mihrud and Khaniqayn were in that part. Finally, Muslims dominated all regions around the Tigris. 
Sa'd Ibn Abi Waqqas was no longer interested in extending the war towards Hulwan and this annoyed some of his troops. So, he ordered an advance as far as Hulwan.  Then, he returned to Kufa and ruled the city for more than three years until he was replaced with 'Ammar Ibn Yasir. According to Ya'qubi, after conquering Ctesiphon, Sa'd came to Kufa and the Jalula attack took place three years later in 19 A.H.  Baladhuri, too, has mentioned the same date , so it seems to be correct.
Now, Muslims had entered Iran from three fronts, on one side, Ctesiphon was in their hands. On the other side, Abu Musa Ash'ari has come towards Ahwaz from Basra. And the third front which had opened by 'Ala' Ibn al-Haďrami in the beginning of 'Umar's rule in Bahrayn and had achieved some success , now had initiated a new move and had made some penetrations in some parts of Fars. 
Given the two latter fronts, Fars which was one Iran's important regions, was now threatened by invasion. Hurmuzan asked Yazdgard to dispatch him to Khuzistan and Fars for protecting those regions so that he could serve as a barrier on the way of Arabs' advance and even gather forces to help Yazdgard. Hurmuzan, along with an army, set off for Tustar (Shushtar). The news of this army reached Muslims and they started a lot of activities to prepare troops.
'Ammar was tasked with joining Abu Musa along with half of the people of Kufa. Before that, Nu'man Ibn Muqarran and thousands of his men had joined Abu Musa. Even 3000 of the 4000-strong Arab border guards who had stayed in Jalula rushed to help. The army of Islam set off towards Tustar. At first, some clashes erupted outside the city and after 1600 Iranians were killed, Hurmuzan was forced to go inside the city and close the gates.
There were also some martyrs on the side of Muslims. One of the well-known martyrs was Bara' Ibn Malik. The city was besieged for some time until one of the city's nobles showed them a secret way to enter the city. 200 Muslims forces broke into the city from that way and after killing the guards, opened the gates on Muslims.
The city was conquered and Hurmuzan took refuge in a palace. He only gave himself up after getting life assurance and under the condition that he would be sent to Medina to the caliph. 'Umar forgave him in Medina until after 'Umar's murder, hi son, 'Ubayd Allah, killed Hurmuzan under the baseless pretext that he had been seen with 'Umar's murderer, Abu Lu'lu', the day before.
After the end of the war, 'Ammar returned to Kufa and Abu Musa continued conquering other cities of Khuzistan such as Susa (Shush). 
At that time, Yazdgard was in Qum, according to Dinwari. He called on all people of Iran to assist him against Arabs who were getting closer every moment. People from Qumis (Damghan), Tabaristan, Gurgan, Damawand, Riy and Isfahan rushed to his help. They gathered a huge army and set off for war against Arab conquerors. 'Ammar wrote the news of this army to 'Umar who called on the people from the pulpit to head for Iraq.
There, 'Uthman asked 'Umar to send the Muslim army from Yemen and Damascus to Iraq. Moreover, he said the caliph, too, should go to Iraq. However, Imam 'Ali opposed this suggestion and said, “This will prompt the Romans to attack Damascus. Also, if Muslims soldiers from Yemen, there will be the threat of an assault from Abyssinia.” Imam opposed the caliph's trip to Iraq because he said Iranians would fight with more fervor if they heard the Arab king's presence. 
At any rate, an army was prepared and its command was given to Nu'man Ibn Muqarran, one of the Companions of Prophet Muhammad (S). It was decided that if he were martyred, Hudhayfa Ibn Yaman, Jarir Ibn 'Abd Allah, Mughira Ibn Shu'ba and Ash'ath Ibn Qays would replace him respectively. Two armies were stationed near Nahawand. Nahawand was located between two fronts of Arabs' war against Iranians, one from Ctesiphon and the other from Ahwaz.
The two armies clashed with each other and fought intensely for four days, from Tuesday to Friday. On the last day, the confrontation was really heavy and despite the martyrdom of Nu'man Ibn Muqarran, the Iranian army was defeated.  This victory was of great significance for Arabs, so it was named “Fath al-Futuh” (the victory of victories).  This battle probably occurred in the year 20 A.H. In this war, a number of Muslim Arabs including their commander was martyred. They were all buried in a graveyard remained in Nahawand's history in memory of the battle's martyrs.
During the years 16 to 20 A.H, conquests continued in northern Iraq as well Muslims advanced as far as Musil, bringing Iraq under their entire control. Among the conquered regions were the cities of Harran, Nusaybin, Qirqisiya' and Samisat and many regions around the Euphrates and the Tigris.
About Iran’s Conquest
The quick conquest of Iran and the fall of the Sassanids dynasty with all its grandeur was a surprising event that cannot be easily explained. Although similar events have occurred in Iran and other world countries and a comparative study of them can help further understanding of realities. In Iraq and Iran, many governments and dynasties, even the long-lived 'Abbasids dynasty, collapsed at the hands of Mongol nomads.
For instance, the Safawids stable and firm for more than 200 years was overthrown by several thousand Ghalzayi Afghans who had come at least 12000 kilometers to reach Isfahan. However, each of these developments must have its particular reasons. Here, it is suitable to quote a source about the political situation of Iran's government after the defeat of Iranian forces against the Roman government in the year 428 A.D.
After Iran's defeat in the war against Rome, Khusraw Parviz looking for scapegoats to blame them for his failure and among them, he decided to execute Shahrbaraz. But before he could carry out his intention, there was a rebellion and Khusraw was imprisoned and then murdered in late February, 628 A.D. Khusraw's son, Shirwayh, ascended to the throne with the title of Kuwad II.
He had joined the insurgents and had agreed with his father's murder. The new king immediately called for peace with Heraclius and accepted to recall the Sassanids armies from Egypt, Palestine, Syria, Asia Minor and western Mesopotamia and recognize the pre-war borders.
It was also agreed that all prisoners of war be extradited and the Swastika and other emblems be returned. Both sides were happy with the end of the war operations which had worn out the two empires for several years. But, Shahrbaraz was dissatisfied over the establishment of peace and he was dangerous as he commanded a large army.
Kuwad II passed away after less than a year in power possibly due to plague and his son, Ardishir III, who was a little child, ascended to the throne. Shahrbaraz decided to claim the throne himself.
So, in June of 629 A.D, backed by Heraclius, he went to Ctesiphon, defeated Ardishir's forces and murdered him along with several of his prominent figures. Shahrbaraz sat on the throne, but his rule didn't last long and he, too, was murdered in less than two months. Also, another claimant in the eastern part of the empire who was Khusraw's nephew, was killed before he could come to the capital with the title of Khusraw III.
As none of Khusraw's sons was left alive, the nobles named his daughter, Puran, as the ruler. Puran was the first woman to ascend to the throne, but she, too, passed away after less than a year in power. A group of kings took power one after the other and each stayed for only a few months. The only thing we know about them is their names as follows, Puran's sister, Adharmidukht; Piruz II, Hurmuz V and Khusraw IV.
Finally, in the year 632 A.D, the nobles named Yazdgard III, the son of Shahriyar and the grandson of Khusraw II, who was almost the last survival of the Sassanids dynasty, to take the throne. Yazdgard lived in virtual hiding in the Istakhr of Fars and it was there that the last Sassanids king was crowned in a fire temple which was named after the first Sassanids king. 
These developments occurred before the start of Iraq's conquest and naturally, they destroyed Iran's political and military structures. It is clear that Yazdgard needed years to put the situation of Iran, which was under domestic and foreign pressure, back on track. But, Arabs' assaults stripped him from such an opportunity and further dealt fatal blows on Iran. The conquest of Iraq located near Ctesiphon, the Sassanids capital, was the first deadly incident which rang the alarm bell for the Sassanids rulers. Those consecutive blows disintegrated that hollow government and shattered it into pieces.
Despite the weakness of the Sassanids government, Iran's defeat cannot be entirely blamed on this incompetence. The Sassanids government did its best, as far as it could. From the Qadisiyya battle to Nahawand's Fath al-Futuh, it tried hard to stop the advancing Arabs. Each time, massive troops were prepared, multiplying the Arabs, but the Iranians' bravery and courage could not resist the will of Arabs who were sure of their victory. The most important point was Arab's faith and their full confidence in the victory of their religion because spreading Islam was their main goal.
Spuler writes, “Today, there is no doubt that the religion of monotheism was the strongest driving force behind Arabs' conquest of lands.”  We should also remember that while fighting for monotheism, Arabs expected booties, too, after victory. They headed for battlefronts after hearing Prophet Muhammad's words who had promised them, the treasures of Caesar and Chosroe. When 'Umar wanted to provoke them, he said,
ÃíåÇ ÇáäÇÓ! Åä Çááå ÚÒ æÌá æÚÏ äÈíå ãÍãÏÇð Õáí Çááå Úáíå æÇáå æÓáã¡ Ãä íÝÊÍ Úáíå ÝÇÑÓ æÇáÑæã¡ æÇááå áÇ íÎáÝ æÚÏå æáÇ íÎÐá ÌäÏå¡ ÝÓÇÑÚæÇ ÑÍãßã Çááå Åáí ÌåÇÏ ÃÚÏÇÆßã ãä ÇáÝÑÓ¡ ÝÅäßã ÈÇáÍÌÇÒ Ýí ÛíÑ ÏÇÑ ãÞÇã æÞÏ æÚÏßã Çááå ÚÒ æÌá ßäæÒ ßÓÑì æÞíÕÑ¡ æÇáãæÇÚíÏ ãä Çááå ÚÒ æÌá ãÖãæäÉ æÃãÑ Çááå ÊÚÇáí ãÝÚæá¡ æÇáÞæá ãä ÑÓæá Çááå Õáí Çááå Úáíå ãÞÈæá¡ æãÇ áã íæÑËßãæå Çááå ÚÒ æÌá Çáíæã¡ íæÑËßãæå ÛÏÇð æÇäßã áä ÊÛäãæÇ ÍÊí ÊÛíÑæÇ æáä ÊÓÔåÏæÇ ÍÊí ÊÞÇÊáæÇ
“O people! The Almighty God certainly promised His Messenger, brought Iran and Rome under his conquest. He keeps His promise and never abandons His troops. God bless thee! Perform a Jihad with Iran's enemies knowing that Hijaz is not a place to stay as He, the Exalted, promised thee riches of Chosroes and Caesaer and be aware that His promises are assured and His decrees are achieved. His Messenger's words are approved as well and what He leaves thee inherited today shall be inherited tomorrow too; thou never attain booties unless thou art changed and never do thou welcome martyrdom unless thou challenge the foes.” 
The tyranny and oppression of the Sassanids government was more or less effective in arousing the people's resentment or in other words, destroying their motivation for defending the Sassanids dynasty.
It led to a reduction of military activities of the Iranian army in the battlefield. Apart from temporary collaboration which may be deemed as treason such as the cooperation of some nobles of Tustar  and Nahawand  in showing the way into the city, the joining of 4000 men from the Qadisiyya army to Arabs cannot be justified as treason.
Baladhuri writes, “4000 men (who were considered among the king's army) from Diylaman who were at the service of the Sassanids government, were in Qadisiyya with Rustam. When the Iranian army was defeated, they were standing at a corner. Feeling they had no shelter, they decided to embrace Islam.
After that, they called on Muslims to let them live wherever they wished and to ally with any tribe they wanted. Sa'd accepted their demand. A chief was chosen for them who were called Hamra' Diylam. Basically, Arabs called non-Arabs “Hamra'”, meaning having a white complexion. These people took part in the conquest of Ctesiphon and the Jalula battle.  There are other examples as well which show that right after Muslims' attacks, some peasants and farmers converted to Islam. 
Qazwini has written, “Treacherous and Arabized Iranians! From the provinces' officials and nearby border guards, threw themselves into the arms of Arabs as soon as they felt the Sassanids dynasty was shaky and the Iranian army had been defeated several times at the hands of the Arab troops.
These Iranians not only helped Arabs in their conquests, but also called on Arab commanders to occupy other Iranian lands which were in their territory and had not been attacked by Arabs yet. They submitted the keys of castles and treasuries to Arabs provided that Arabs would let them stay in power in some regions.” 
The late Jalal Al Ahmad writes, “Before Islam came to confront us, we invited it. Let's forget about Rustam Farrukhzadi who desperately defended the Sassanids ferocity and the Zoroastrians' backward traditions. But, the people, Ctesiphon went into their alleys with bread and dates to welcome the Arabs who went to plunder the king's palace and the carpet of Baharistan. 
The proper treatment of victorious Arabs with the people of the cities they conquered, could encourage the people towards the sincerity of Muslims. Peace accords did not force the people into abandoning their religion and traditions. Even there was no emphasis on destroying the fire temples. The tax paid was, in most cases, less than what was received by the Sassanids government and the provincial governors from the people.
So, what reason could they have to sacrifice their lives for the Sassanids rulers. It has been said in this regard, “The peace accords of Arab armies with different town and cities, which in many cases, entailed much lighter obligations for the people compared to the taxes paid previously to the central Sassanids government, urged many Iranian to give up. They were not interested in fighting for a court that did not pay any attention to them. We should welcome the new gods who take lower taxes instead of fighting against them. This was the psychology of many Iranians.” 
 Futuh al-Buldan, p. 137
 Ibid p. 140
 Ibid p. 141
 Ibid p. 141-142
 al-Uns al-jalil, vol. I, p. 126
 al-Uns al-jalil p. 250
 Futuh al-Buldan, p. 145 (some people have said that ‘Umar traveled to Damascus four times during his caliphate ) Futuh Misr wa Akhbaruha, p. 56 (footnote
 al-Uns al-jalil, vol. I, pp 253-254
 Ibid pp 256-257
 Futuh al-Buldan, p. 146
 Tarikh Khalifat Ibn Khayyat, p. 157
 Futuh al-Buldan, p. 148
 Ibid p. 151
 Futuh Misr wa Akhbaruha, p. 53
 Futuh Misr wa Akhbaruha, pp 57-58
 Atlas Tarikh al-Islam, p. 133
 One said to another, Çä åÄáÇÁ ÇáÞæã áÇ íÊæÌåæä Çáì ÃÍÏ ÇáÇ ÙåÑæÇ Úáíå
“These people declare war with no one but when they overcome” Futuh Misr wa Akhbaruha, pp 59
 Ibid p. 61
 Futuh Misr wa Akhbaruha p. 129
 Tarikh at-Tabari, vol. III, p. 570
 Ibid vol. III, p. 601
 Ibid vol. III, p. 464
 Futuh al-Buldan, p. 143
 al-Futuh, vol. I, pp 143-144
 Tarikh Tamaddun, vol. IV, p. 64; Ash-Sham fi Sadr al-Islam, pp 63-64, footnote
 See the list in, Ash-Sham fi Sadr al-Islam, pp 60-70
 al-Futuh, vol. I, p. 165
 Futuh al-Buldan, p. 251; Akhbar al-Tiwal, p. 113
 Tarikh Iran, Cambridge (persian translation), vol. IV, p. 15
 al-Futuh, vol. I, p. 170
 Akhbar al-Tiwal, p. 114; Atlas Tarikh al-Islam, p. 128 The author made a mistake about the fact that the king, in this time, regarded Iran as the city of Buraz, next, Shiriwayh and then Buran In essence, Yazdgard, since 632, succeeded them and conquering Iraq began from his time
 Akhbar al-Tiwal, p. 114
 In time of war, Jarir Ibn ‘Abd Allah Bijili promised his tribesmen that they would be the only Arabs to be benefited much in case this city were to be entered Akhbar al-Tiwal, p. 115
 Akhbar al-Tiwal, p. 114; Ibn A‘tham (Al-Futuh, vol. I, p. 168) says that Mihrdad has been king of Adharbayjan
 Akhbar al-Tiwal, p. 115
 Akhbar al-Tiwal, p. 116
 Ibid p. 117
 al-Tariq Ila l-Mada’in, p. 213
 Mu‘jam al-Buldan, vol. II, p. 363
 Ibid vol. I, p. 432
 Akhbar al-Tiwal, p. 117
 Mu‘jam al-Buldan, vol. I, p. 430
 Mu‘jam al-Buldan, vol.I, p.432.
 Tabaqat al-Kubra, vol. VII, p. 7
 al-Futuh, vol. I, p. 201
 Muruj al-dhahab, vol. II, p. 310
 Akhbar al-Tiwal, p. 121
 Tarikh Iran, Cambridge (persian translation), vol. IV, p. 17
 Akhbar al-Tiwal, p. 119 (he mentions the forces to be twenty thousand people but he further refers to the troops joining him from Basra and other places ) Al-Futuh, vol. I, p. 175 (there, there is a census of tribal people
 Akhbar al-Tiwal, p. 120
 Ibid pp 120-121 (This was exactly referred when Rostam spoke with Mughira
 al-Futuh, vol. I, p. 197 (Ibn A‘tham mentions the exact speech of the king in Persian
 Ibn A‘tham cites the names in a different way al-Futuh, vol. I, p. 20
 Akhbar al-Tiwal, p. 123 (Dinwari mentions his very calling “a man of challenge” in Persian )
 Futuh al-Buldan, p. 259
 Ibid p. 260
 Tarikh at-Tabari, vol. III, p. 590; Muruj al-dhahab, vol. III, p. 319
 al-Qadisiyya, pp 216-232
 Muruj al-dhahab, vol. III, p. 319
 Mu‘jam al-Buldan, vol. IV, pp 490-491
 ‘Umar wrote to Sa‘d, Arabs resemble camels, wherever camels lay well, Arabs find it well too Futuh al-Buldan, p. 275
 Futuh al-Buldan, p. 275
 Mu‘jam al-Buldan, vol. IV, p. 491
 Futuh al-Buldan, p. 287; al-Futuh, vol. I, p. 288
 Akhbar al-Tiwal, p. 126; Futuh al-Buldan, p. 262
 Tarikh Iran, Cambridge (persian translation), vol. IV, p. 18 Yaqut speaks of seven-fold cities of Mada’in this way, Isfabur (Isfanbar), Wah Ardishir (Bihrsir), Hanbushafur (Jundishabur), Darznidan (Darzijan), Wah Jundyu Khusruw (Rumiyya), Nunyafaj and Kirdafadh (His mentioned names slightly differ from what has been quoted from Tarikh Iran ) He adds, Mada’in, in our time, is a village six leagues far from Baghdad Citizens are mainly farmers and followers of Imam ‘Ali (a) Salman Farsi’s tombstone rests in eastern Medina Mu‘jam al-Buldan, vol. V, p. 75
 al-Futuh, vol. I, p. 212
 Akhbar al-Tiwal, p. 216; Futuh al-Buldan, p. 262
 Akhbar al-Tiwal, p. 127
 Futuh al-Buldan, p. 263
 al-Futuh, vol. I, p. 278
 Akhbar al-Tiwal, p. 129
 Futuh al-Buldan, p. 264
 al-Futuh, vol. I, p. 279-280
 Tarikh al-Ya’qubi, vol. II, p. 151
 Futuh al-Buldan, p. 265
 al-Bad’ wa l-Tarikh, vol. V, p. 183
 Akhbar al-Tiwal, p. 133
 Akhbar al-Tiwal, pp 130-132
 Akhbar al-Tiwal, pp 134-135
 Ibid pp 136-137
 al-Bad’ wa l-Tarikh, vol. V, p. 182
 Tarikh Iran, Cambridge (persian translation), vol. III, p. 267
 Tarikh Iran, vol. I, p. 7
 al-Futuh, vol.I, p.165.
 Akhbar al-Tiwal, p. 131
 Ibid p. 137
 Futuh al-Buldan, p. 279
 Spuler, Tarikh Iran, vol. I, p. 17
 Bist Maqalih Qazwin quoted from, Khadamat Mutaqabil Iran wa Islam, p. 79
 Gharbzadigi, p. 48
 Tarikh Iran, Cambridge (persian translation), vol. III, part I, p. 271