Muslim Conquest of Persia

Since the 1st century BCE, the border between the Roman (later Byzantine) and Parthian (later Sassanid) empires had been the Euphrates River. The border was constantly contested. Most battles, and thus most fortifications, were concentrated in the hilly regions of the north, as the vast Arabian or Syrian Desert (Roman Arabia) separated the rival empires in the south. The only dangers expected from the south were occasional raids by nomadic Arab tribesmen. Both empires therefore allied themselves with small, semi-independent Arab principalities, which served as buffer states and protected Byzantium and Persia from Bedouin attacks. The Byzantine clients were the Ghassanids; the Persian clients were the Lakhmids. The Ghassanids and Lakhmids feuded constantly, which kept them occupied, but that did not greatly affect the Byzantines or the Persians. In the 6th and 7th centuries, various factors destroyed the balance of power that had held for so many centuries. The conflict with the Byzantines greatly contributed to its weakness, by draining Sassanid resources, leaving it a prime target for the Muslims.

The Byzantine–Sasanian War of 602–628 was the final and most devastating of the series of wars fought between the Byzantine Empire and the Sasanian Empire of Iran. This became a decades-long conflict, the longest war in the series, and was fought throughout the Middle East: in Egypt, the Levant, Mesopotamia, the Caucasus, Anatolia, Armenia, the Aegean Sea and before the walls of Constantinople itself.

By the end of the conflict, both sides had exhausted their human and material resources and achieved very little. Consequently, they were vulnerable to the sudden emergence of the Islamic Rashidun Caliphate, whose forces invaded both empires only a few years after the war.

After the Ridda wars, a tribal chief of northeastern Arabia, Al-Muthanna ibn Haritha, raided the Sasanian towns in Mesopotamia (modern-day Iraq). With the success of the raids, a considerable amount of booty was collected. Al-Muthanna ibn Haritha went to Medina to inform Abu Bakr about his success and was appointed commander of his people, after which he began to raid deeper into Mesopotamia. Using the mobility of his light cavalry, he could easily raid any town near the desert and disappear again into the desert, beyond the reach of the Sasanian army. Al-Muthanna's acts made Abu Bakr think about the expansion of the Rashidun Empire.

To ensure victory, Abu Bakr made two decisions concerning the attack on Persia: first, the invading army would consist entirely of volunteers; and second, to put his best general, Khalid ibn al-Walid, in command. After defeating the self-proclaimed prophet Musaylimah in the Battle of Yamama, Khalid was still at Al-Yamama when Abu Bakr ordered him to invade the Sassanid Empire. Making Al-Hirah the objective of Khalid, Abu Bakr sent reinforcements and ordered the tribal chiefs of northeastern Arabia, Al-Muthanna ibn Haritha, Mazhur bin Adi, Harmala and Sulma to operate under Khalid's command. Around the third week of March 633 (first week of Muharram 12th Hijrah) Khalid set out from Al-Yamama with an army of 10,000. The tribal chiefs, with 2,000 warriors each, joined him, swelling his ranks to 18,000.

The Battle of Sallasil or the Battle of Chains was the first battle fought between the Rashidun Caliphate and the Sasanian Persian Empire. The battle was fought in Kazima (present day Kuwait) soon after the Ridda Wars were over and Eastern Arabia was united under the authority of Caliph Abu Bakr. It was also the first battle of the Rashidun Caliphate in which the Muslim army sought to extend its frontiers.

The Battle of River also known as Battle of Al Madhar took place in Mesopotamia (Iraq) between the forces of the Rashidun Caliphate and the Sasanian Empire. Muslims, under Khalid ibn al-Walid's command, defeated the numerically superior Persian army.

The Battle of Walaja was a battle fought in Mesopotamia (Iraq) in May 633 between the Rashidun Caliphate army under Khalid ibn al-Walid and Al-Muthanna ibn Haritha against the Sassanid Empire and its Arab allies. In this battle the Sassanid army is said to have been two times the size of the Muslim army. Khalid decisively defeated the numerically superior Sassanian forces using a variation of the double envelopment tactical manoeuvre, similar to the manoeuvre Hannibal used to defeat the Roman forces at the Battle of Cannae; however, Khalid is said to have developed his version independently.

The Battle of Ullais was fought between the forces of the Rashidun Caliphate and the Sassanid Persian Empire in the middle of May 633 CE in Iraq, and is sometimes referred to as the Battle of Blood River since, as a result of the battle, there were enormous amounts of Sassanian and Arab Christian casualties. This was now the last of four consecutive battles that were fought between invading Muslims and the Persian army. After each battle, the Persians and their allies regrouped and fought again. These battles resulted in the retreat of the Sassanid Persian army from Iraq and its capture by Muslims under the Rashidun Caliphate.

The Battle of Hira was fought between the Sasanian Empire and the Rashidun Caliphate in 633. It was one of the early battles of the Muslim conquest of Persia, and the loss of the frontier city on the Euphrates River opened the way to the Sasanian capital at Ctesiphon on the Tigris River.

The Battle of Ayn al-Tamr took place in modern-day Iraq (Mesopotamia) between the early Muslim Arab forces and the Sassanians along with their Arab Christian auxiliary forces. The Muslims under Khalid ibn al-Walid's command soundly defeated the Sassanian auxiliary force, which included large numbers of non-Muslim Arabs who broke earlier covenants with the Muslims. According to non-Muslim sources, Khalid ibn al-Walid captured the Arab Christian commander, Aqqa ibn Qays ibn Bashir, with his own hands.

Then Khalid instructed the entire forces to storm the city of Ayn al-Tamr and slaughter the Persian inside the garrison after they breached. After the city has been subdued, some Persians had hoped that the Muslim commander, Khalid ibn al-Walid, would be "like those Arabs who would raid [and withdraw].".

However, Khalid continued to press further against the Persians and their allies in the subsequent Battle of Dawmat al-Jandal, while he left two of his deputy, Al-Qa'qa' ibn Amr al-Tamimi and Abu Layla, to lead a separate forces in order to intercept another Persian-Arab christians enemy coming from east, which led to the Battle of Husayd

Battle of Al-Anbar was between the Muslim Arab army under the command of Khalid ibn al-Walid and the Sasanian Empire. The battle took place at Anbar which is located approximately 80 miles from the ancient city of Babylon. Khalid besieged the Sassanian Persians in the city fortress, which had strong walls. Scores of Muslim archers were used in the siege. The Persian governor, Shirzad, eventually surrendered and was allowed to retire. The Battle of Al-Anbar is often remembered as the "Action of the Eye" since Muslim archers used in the battle were told to aim at the "eyes" of the Persian garrison.

The Battle of Daumat-ul-jandal took place between Muslims and Rebel Arab tribes in August 633 CE. This was a part of the Riddah wars. Daumat ul jandal was given to Iyad ibn Ghanm to crush the rebels, but he failed in doing so, and send for help to Khalid ibn Walid who was in Iraq in those days. Khalid went there and defeated the rebels.

The Battle of Husayd was a battle between Rashidun caliphate army under Al-Qa'qa' ibn Amr al-Tamimi against the warriors of Arab Christian and Sasanid army of 633 CE. Rashidun army defeated the coalition army in decisive battle and all the coalition commanders fell in battle.

Bahman had organised a new army, made up partly of the survivors of the Battle of Ullais, partly of veterans drawn from garrisons in other parts of the Byzantine Empire, and partly of fresh recruits. This army was now ready for battle. Apart from the defeat at the Battle of Ayn al-Tamr, the incensed Arabs of this area also sought revenge for the killing of their great chief, Aqqa ibn Qays ibn Bashir. They were anxious, too, to regain the lands which they had lost to the Muslims, and to free the comrades who had been captured by the invaders. A large number of clans began to prepare for war.

Khalid decided to fight and destroy each imperial force separately. The exact location of the imperial camp at Muzayyah had been established by Khalid's agents. To deal with this objective he designed a manoeuvre which, seldom practised in history, is one of the most difficult to control and co-ordinate-a simultaneous converging attack from three directions made at night.

Khalid ibn al-Walid issued orders for the move. The three corps would march from their respective locations at Husaid, Khanafis and Ain-ut-Tamr along separate routes he had specified and meet on a given night and at a given hour at a place a few miles short of Muzayyah. This move was carried out as planned, and the three corps concentrated at the appointed place. He laid down the time of the attack and the three separate directions from which the three corps would fall upon the unsuspecting enemy. The imperial army knew of the attack only when three roaring masses of Muslim warriors hurled themselves at the camp. In the confusion of the night the imperial army never found its feet. Terror became the mood of the camp as soldiers fleeing from one Muslim corps ran into another. Thousands were slaughtered. The Muslims tried to finish this army, but large numbers of Persians and Arabs nevertheless managed to get away, helped by the very darkness that had cloaked the surprise attack.

The Battle of Saniyy was a strategic engagement between the Muslim Arab forces led by Khalid ibn al-Walid and the Sasanian Empire, supplemented by their Christian Arab allies, during the early Islamic conquests. Following victories at Muzayyah and other locations, Khalid ibn al-Walid targeted Saniyy, aiming to prevent the Sasanian and Christian Arab forces from consolidating.

In response to Muslim advances, Bahman, a Sasanian commander, organized a new army comprising survivors from previous battles, garrison veterans, and new recruits. Despite being less experienced, this force was augmented by Christian Arab tribes, motivated by losses at Ayn al-Tamr and the death of their chief, Aqqa. They sought to reclaim lost territories and liberate captured comrades. Bahman strategically divided his forces, dispatching them to Husaid and Khanafis, while awaiting the readiness of the Christian Arab contingents for a coordinated assault.

Khalid, anticipating the threat of a unified enemy force, preemptively divided his forces to engage the enemy separately, successfully implementing a strategy of divide and conquer. He deployed his troops to Ain-ul-Tamr, organizing them into three corps and planning simultaneous attacks on the dispersed enemy forces. Despite logistical challenges, Khalid's forces achieved victories at Husaid and Khanafis, forcing the remaining enemy to retreat and regroup with the Christian Arabs at Muzayyah.

Subsequently, Khalid executed a coordinated night attack on Saniyy in the second week of November 633 CE, employing a three-pronged assault that overwhelmed the defenders. The battle resulted in significant losses for the Christian Arab forces, including the death of their commander, Rabi'a bin Bujair. Women, children, and youths were spared and taken captive. Following this victory, Khalid swiftly moved to neutralize the remaining forces at Zumail, effectively ending Persian influence in Iraq and securing the region for the Muslims.

The battle of Zumail was fought in 633 CE in Mesopotamia (what is now Iraq). It was a major Muslim victory in their conquest of that area. Under cover of night the Arab Muslims attacked the Christian-Arab forces, loyal to the Sasanian Empire, from three different sides. The Christian-Arab forces were unable to withstand the Muslim's surprise attack and soon dispersed but failed to escape from the battlefield and became the victims of a three sided attack by Khalid ibn al-Walid's army. At Zumail nearly the whole Christian Arab army was slaughtered by Khalid's Corps. These battles ended Persian control in Mesopotamia, which finally fell to the Islamic Caliphate.

The Battle of Firaz was the last battle of the Muslim Arab commander Khalid ibn al-Walid in Mesopotamia (Iraq) against the combined forces of the Byzantine Empire and the Sasanian Empire.

According to the will of Abu Bakr, Umar was to continue the conquest of Syria and Mesopotamia. On the northeastern borders of the Empire, in Mesopotamia, the situation was rapidly deteriorating. During Abu Bakr's era, Khalid ibn al-Walid had left Mesopotamia with half his army of 9000 soldiers to assume command in Syria, whereupon the Persians decided to take back their lost territory. The Muslim army was forced to leave the conquered areas and concentrate on the border. Umar immediately sent reinforcements to aid Muthanna ibn Haritha in Mesopotamia under the command of Abu Ubaid al-Thaqafi. At that time, a series of battles between the Persians and Arabs occurred in the region of Sawad, such as Namaraq, Kaskar and Baqusiatha, in which the Arabs managed to maintain their presence in the area. Later on, the Persians defeated Abu Ubaid in the Battle of the Bridge. It is traditionally dated to the Year 634, and was the only major Sassanian victory over the invading Muslim armies.

Battle of the Bridge was a decisive Sasanian victory which gave them a huge boost to expel invading Arabs from Mesopotamia. Thus, they advanced with a huge army to fight the remnants of the Muslim army near Kufa on the Euphrates. Caliph Umar sent reinforcements to the region which were mainly the people who were fighting Muslims during the Ridda wars. Al-Muthanna ibn Haritha managed to force the upcoming Persian army to cross the river to a place where his soldiers, who were divided into Brigades, could encircle their numerically superior opponents. The war ended with a huge success for the Muslims, thanks in no small part to the help of local Christian Arab tribes who decided to help the Muslim army. The Arabs gained the momentum to further expand their wars against the Sassanids and their allies.

In 635 Yazdgerd III sought an alliance with Emperor Heraclius of the Eastern Roman Empire, marrying the latter's daughter (or, by some traditions, his granddaughter) in order to seal the arrangement. While Heraclius prepared for a major offence in the Levant, Yazdegerd ordered the concentration of massive armies to push the Muslims out of Mesopotamia for good through a series of well-coordinated attacks on two fronts.

Umar ordered his army to retreat to the Arabian border and began raising armies at Medina for another campaign into Mesopotamia. Umar appointed Saad ibn Abi Waqqas, a respected senior officer. Saad left Medina with his army in May 636 and arrived at Qadisiyyah in June.

While Heraclius launched his offensive in May 636, Yazdegerd was unable to muster his armies in time to provide the Byzantines with Persian support. Umar, allegedly aware of this alliance, capitalized on this failure: not wanting to risk a battle with two great powers simultaneously, he quickly moved to reinforce the Muslim army at Yarmouk to engage and defeat the Byzantines. Meanwhile, Umar ordered Saad to enter into peace negotiations with Yazdegerd III and invite him to convert to Islam to prevent Persian forces from taking the field. Heraclius instructed his general Vahan not to engage in battle with the Muslims before receiving explicit orders; however, fearing more Arab reinforcements, Vahan attacked the Muslim army in the Battle of Yarmouk in August 636, and was routed.

With the Byzantine threat ended, the Sassanid Empire was still a formidable power with vast manpower reserves, and the Arabs soon found themselves confronting a huge Persian army with troops drawn from every corner of the empire, including war elephants, and commanded by its foremost generals. Within three months, Saad defeated the Persian army in the Battle of al-Qādisiyyah, effectively ending Sassanid rule west of Persia proper. This victory is largely regarded as a decisive turning point in Islam's growth:

After a Muslim victory in the Battle of al-Qādisiyyah, the Caliph Umar ruled that it was time to conquer the Sasanian Empire's capital of Ctesiphon. Battle of Babylon was fought between the forces of Sassanid Empire and Rashidun Caliphate in 636. Muslim Arabs won the encounter to maintain their pursuit of conquering Ctesiphon.

By mid-December of 636, Muslims gained the Euphrates and camped outside Babylon. The Sassanian forces in Babylon are said to have been commanded by Piruz Khosrow, Hormuzan, Mihran Razi and Nakhiragan. Whatever the reason, it is in fact that the Sassanids were unable to oppose a significant resistance to the Muslims. Hormuzan withdrew with his forces to his province of Ahwaz, after which the other Persian generals returned their units and retreated to the north. After the withdrawal of Sassanian forces, citizens of Babylon formally surrendered.

The Siege of Ctesiphon took place from January to March, 637 between the forces of Sassanid Empire and Rashidun Caliphate. Ctesiphon, located on the eastern bank of the Tigris, was one of the great cities of Persia, the imperial capital of the Parthian and Sassanid Empires. The Muslims managed to capture Ctesiphon ending the Persian rule over Mesopotamia.

In December 636, Umar ordered Utbah ibn Ghazwan to head south to capture al-Ubulla (known as "port of Apologos" in the Periplus of the Erythraean Sea) and Basra, in order to cut ties between the Persian garrison there and Ctesiphon. Utbah ibn Ghazwan arrived in April 637, and captured the region. The Persians withdrew to the Maysan region, which the Muslims seized later as well.

After withdrawal from Ctesiphon, the Persian armies gathered at Jalula north-east of Ctesiphon, a place of strategic importance from where routes led to Iraq, Khurasan and Azerbaijan. The Caliph decided to deal with Jalula first; his plan was first to clear the way north before any decisive action against Tikrit and Mosul. Some time in April 637, Hashim marched at the head of 12,000 troops from Ctesiphon and after defeating the Persians at the Battle of Jalula, laid siege to Jalula for seven months, until it surrendered on the usual terms of Jizya.

In December 636, Umar ordered Utbah ibn Ghazwan to head south to capture al-Ubulla (known as "port of Apologos" in the Periplus of the Erythraean Sea) and Basra, in order to cut ties between the Persian garrison there and Ctesiphon. Utbah ibn Ghazwan arrived in April 637, and captured the region. The Persians withdrew to the Maysan region, which the Muslims seized later as well.

The Muslim invasion of Fars began in 638/9, when the Rashidun governor of Bahrain, al-'Ala' ibn al-Hadrami, having defeated some rebellious Arab tribes, seized an island in the Persian Gulf. Although al-'Ala' and the rest of the Arabs had been ordered to not invade Fars or its surrounding islands, he and his men continued their raids into the province. Al-'Ala quickly prepared an army which he divided into three groups, one under al-Jarud ibn Mu'alla, the second under al-Sawwar ibn Hammam, and the third under Khulayd ibn al-Mundhir ibn Sawa.

When the first group entered Fars, it was quickly defeated and al-Jarud was killed. The same thing soon happened to the second group. However, the third group was more fortunate: Khulayd managed to keep the defenders at bay, but was unable to withdraw to Bahrain, as the Sassanians were blocking his way to the sea. Umar, having found out about al-'Ala's invasion of Fars, had him replaced with Sa'd ibn Abi Waqqas as governor. Umar then ordered Utbah ibn Ghazwan to send reinforcements to Khulayd. Once the reinforcements arrived, Khulayd and some of his men managed to withdraw to Bahrain, while the rest withdrew to Basra.

After the conquest of Khuzistan, Umar wanted peace.;Though considerably weakened, the image of the Persian Empire as a fearsome superpower still resonated in the minds of the newly-ascendant Arabs, and Umar was wary of unnecessary military engagement with it, preferring to leave the rump of the Persian Empire alone.

After the defeat of the Persian forces at the Battle of Jalula in 637, Yazdgerd III went to Rey and from there moved to Merv, where he set up his capital and directed his chiefs to conduct continuous raids in Mesopotamia. Within four years, Yazdgerd III felt powerful enough to challenge the Muslims again for control of Mesopotamia. Accordingly, he recruited 100,000 hardened veterans and young volunteers from all parts of Persia, under the command of Mardan Shah, which marched to Nahavand for the last titanic struggle with the Caliphate.

The Battle of Nahavand was fought in 642 between Arab Muslims and Sassanid armies. The battle is known to Muslims as the "Victory of Victories." The Sassanid King Yazdegerd III escaped to the Merv area, but was unable to raise another substantial army. It was a victory for the Rashidun Caliphate and the Persians consequently lost the surrounding cities including Spahan (renamed Isfahan).

Umar decided to strike the Persians immediately after their defeat at Nahavand, while he still possessed a psychological advantage. Umar had to decide which of three provinces to conquer first: Fars in the south, Azerbaijan in the north or Isfahan in the center. Umar chose Isfahan, as it was the heart of the Persian Empire and a conduit for supply and communications among the Sassanid garrisons, and its capture would isolate Fars and Azerbaijan from Khorasan, Yazdegerd's stronghold. After he had taken Fars and Isfahan, the next attacks would be simultaneously launched against Azerbaijan, the northwestern province, and Sistan, the easternmost province of the Persian Empire. The conquest of those provinces would leave Khorasan isolated and vulnerable, the last stage of the conquest of Sassanid Persia.

Preparations were complete by January 642. Umar appointed Abdullah ibn Uthman as commander of the Muslim forces for the invasion of Isfahan. From Nahavand, Nu'man ibn Muqaarin marched to Hamadan, and then proceeded 370 kilometres (230 mi) southeast to the city of Isfahan, defeating a Sasanian army there. The enemy commander, Shahrvaraz Jadhuyih, along with another Sasanian general, was killed during the battle. Nu'man, reinforced by fresh troops from Busra and Kufa under the command of Abu Musa Ashaari and Ahnaf ibn Qais, then besieged the city. The siege continued for a few months before the city surrendered.

The Muslims had conquered Byzantine Armenia in 638–639. Persian Armenia, north of Azerbaijan, remained in Persian hands, along with Khurasan. Umar refused to take any chances; he never perceived the Persians as being weak, which facilitated the speedy conquest of the Persian Empire. Again Umar sent simultaneous expeditions to the far north-east and north-west of the Persian Empire, one to Khurasan in late 643 and the other to Armenia. Bukair ibn Abdullah, who had recently subdued Azerbaijan, was ordered to capture Tiflis. From Bab, on the western coast of the Caspian Sea, Bukair continued his march north. Umar employed his traditional successful strategy of multi-pronged attacks. While Bukair was still kilometres away from Tiflis, Umar instructed him to divide his army into three corps. Umar appointed Habib ibn Muslaima to capture Tiflis, Abdulrehman to march north against the mountains and Hudheifa to march against the southern mountains. With the success of all three missions, the advance into Armenia came to an end with the death of Umar in November 644. By then almost the whole of the South Caucasus was captured.

In 644, al-'Ala' once again attacked Fars from Bahrain, reaching as far as Estakhr, until he was repulsed by the Persian governor (marzban) of Fars, Shahrag. Some time later, Uthman ibn Abi al-As managed to establish a military base at Tawwaj, and soon defeated and killed Shahrag near Rew-shahr.

In 648, 'Abd-Allah ibn al-'Ash'ari forced the governor of Estakhr, Mahak, to surrender the city. However, the inhabitants of the city would later rebel in 649/650 while its newly appointed governor, 'Abd-Allah ibn 'Amir, was trying to capture Gor. The military governor of Estakhr, 'Ubayd Allah ibn Ma'mar, was defeated and killed. In 650/651, Yazdegerd went there to plan an organized resistance against the Arabs, and, after some time, went to Gor. However, Estakhr failed to put up a strong resistance, and was soon sacked by the Arabs, who killed over 40,000 defenders. The Arabs then quickly seized Gor, Kazerun and Siraf, while Yazdegerd fled to Kerman. Muslim control of Fars remained shaky for a time, with several local rebellions following the conquest.

The conquest of Iranian Azerbaijan started in 651, part of a simultaneous attack launched against Kerman and Makran in the southeast, against Sistan in the northeast and against Azerbaijan in the northwest. Hudheifa marched from Rey in central Persia to Zanjan, a well-fortified Persian stronghold in the north. The Persians came out of the city and gave battle, but Hudheifa defeated them, captured the city, and those who sought peace were granted it on the usual jizya conditions.

Hudheifa then continued his march north along the western coast of the Caspian Sea and captured Bab al-Abwab by force. At this point Hudheifa was recalled by Uthman, to be replaced by Bukair ibn Abdullah and Utba ibn Farqad. They were sent to carry out a two-pronged attack against Azerbaijan: Bukair along the western coast of the Caspian Sea, and Uthba into the heart of Azerbaijan.

On his way north Bukair was halted by a large Persian force under Isfandiyar, the son of Farrukhzad. A pitched battle was fought, after which Isfandiyar was defeated and captured. In return for his life, he agreed to surrender his estates in Azerbaijan and persuade others to submit to Muslim rule. Uthba ibn Farqad then defeated Bahram, brother of Isfandiyar. He too sued for peace. Azerbaijan then surrendered to Caliph Umar, agreeing to pay the annual jizya.

Khorasan was the second-largest province of the Sassanid Empire. It stretched from what is now northeastern Iran, northwestern Afghanistan and southern Turkmenistan. In 651 the conquest of Khurasan was assigned to Ahnaf ibn Qais.

Ahnaf marched from Kufa and took a short and less frequented route via Rey and Nishapur. Rey was already in Muslim hands and Nishapur surrendered without resistance. From Nishapur, Ahnaf marched to Herat in western Afghanistan. Herat was a fortified town, and the resulting siege lasted for a few months before it surrendered, bringing the whole of southern Khorasan under Muslim control. Ahnaf then marched north directly to Merv, in present-day Turkmenistan. Merv was the capital of Khurasan and here Yazdegred III held his court. On hearing of the Muslim advance, Yazdegerd III left for Balkh. No resistance was offered at Merv, and the Muslims occupied the capital of Khurasan without a fight. Ahnaf stayed at Merv and waited for reinforcement from Kufa. Meanwhile, Yazdegerd had also gathered considerable power at Balkh and allied with the Turkic Khan of Farghana, who personally led the relief contingent. Umar ordered Ahnaf to break up the alliance. The Khan of Farghana, realizing that fighting against the Muslims might endanger his own kingdom, withdrew from the alliance and pulled back to Farghana.

The remainder of Yazdegerd's army was defeated at the Battle of Oxus River and retreated across the Oxus to Transoxiana. Yazdegerd himself narrowly escaped to China.The Muslims had now reached the outermost frontiers of Persia. Beyond that lay the lands of the Turks and still further lay China. Ahnaf returned to Merv and sent a detailed report of his success to the anxiously-waiting Umar, and sought permission to cross the Oxus river and invade Transoxiana. Umar ordered Ahnaf to stand down and instead consolidate his power south of the Oxus.