Most traditional accounts have the first Muslim armies deploy to Syria from Medina at the beginning of 13 AH (early spring 634). The commanders of the Muslim armies were Amr ibn al-As,
Yazid ibn Abi Sufyan, Shurahbil ibn Hasana and Abu Ubayda ibn al-Jarrah, though the last may have not deployed to Syria until after Umar's succession to the caliphate in the summer of 634, following Abu Bakr's death. According to Donner, the traditional sources' dating of the first Muslim armies' deployment to Syria was behind by several months. It most likely occurred in the autumn of 633, which better conforms with the anonymous
Syriac Chronicle of 724, which dates the first clash between the Muslim armies and the Byzantines to February 634. By the time Khalid had left Iraq, the Muslim armies in Syria had already fought a number of skirmishes with local Byzantine garrisons and dominated the southern Syrian countryside, but did not control any urban centers. Khalid was appointed supreme commander of the Muslim armies in Syria. Accounts cited by al-Baladhuri, al-Tabari,
Ibn A'tham,
al-Fasawi (d. 987) and Ibn Hubaysh al-Asadi hold that Abu Bakr appointed Khalid supreme commander as part of his reassignment from Iraq to Syria, citing the general's military talents and record. A single account in al-Baladhuri instead attributes Khalid's appointment to a consensus among the commanders already in Syria, though Athamina asserts "it is inconceivable that a man like [Amr ibn al-As] would agree" to such a decision voluntarily. Upon his accession, Umar may have confirmed Khalid as supreme commander. Khalid reached the meadow of
Marj Rahit north of
Damascus after his army's trek across the desert. He arrived on
Easter day of that year, i.e. 24 April 634, a rare precise date cited by most traditional sources, which Donner deems to be likely correct. There, Khalid
attacked a group of Ghassanids celebrating Easter before he or his subordinate commanders raided the
Ghouta agricultural belt around Damascus. Afterward, Khalid and the commanders of the earlier Muslim armies, except for Amr, assembled at
Bosra southeast of Damascus. The trading center of Bosra, along with the
Hauran region in which it lies, had historically supplied the nomadic tribes of Arabia with wheat, oil and wine and had been visited by Muhammad during his youth. The Byzantines may not have reestablished an imperial garrison in the city in the aftermath of the Sasanian withdrawal in 628 and the Muslim armies encountered token resistance during their siege. Bosra capitulated in late May 634, making it the first major city in Syria to fall to the Muslims. Khalid and the Muslim commanders headed west to Palestine to join Amr as the latter's subordinates in the
Battle of Ajnadayn, the first major confrontation with the Byzantines, in July. The battle ended in a decisive victory for the Muslims and the Byzantines retreated toward
Pella ('Fahl' in Arabic), a major city east of the
Jordan River. The Muslims pursued them and scored another major victory at the
Battle of Fahl, though it is unclear if Amr or Khalid held overall command in the engagement.
Siege of Damascus in 636. The remnants of the Byzantine forces from Ajnadayn and Fahl retreated north to Damascus, where the Byzantine commanders called for imperial reinforcements. Khalid advanced, possibly besting a Byzantine unit at the
Marj al-Suffar plain before besieging the city. Each of the five Muslim commanders were charged with blocking one of the city gates; Khalid was stationed at
Bab Sharqi (the East Gate). A sixth contingent positioned at
Barzeh immediately north of Damascus repulsed relief troops dispatched by the Byzantine emperor
Heraclius (). Several traditions relate the Muslims' capture of Damascus. The most popular narrative is preserved by the Damascus-based
Ibn Asakir (d. 1175), according to whom Khalid and his men breached the Bab Sharqi gate. Khalid and his men scaled the city's eastern walls and killed the guards and other defenders at Bab Sharqi. As his forces entered from the east, Muslim forces led by Abu Ubayda had entered peacefully from the western
Bab al-Jabiya gate after negotiations with Damascene notables led by
Mansur ibn Sarjun, a high-ranking city official. The Muslim armies met up in the city center where capitulation terms were agreed. On the other hand, al-Baladhuri holds that Khalid entered peacefully from Bab Sharqi while Abu Ubayda entered from the west by force. Modern research questions Abu Ubayda's arrival in Syria by the time of the siege. Caetani cast doubt about the aforementioned traditions, while the orientalist
Henri Lammens substituted Abu Ubayda with Yazid ibn Abi Sufyan. In the versions of the Syriac author
Dionysius of Tel Mahre (d. 845) and the
Melkite patriarch
Eutychius of Alexandria (d. 940), the Damascenes led by Mansur, having become weary of the siege and convinced of the besiegers' determination, approached Khalid at Bab Sharqi with an offer to open the gate in return for assurances of safety. Khalid accepted and ordered the drafting of a capitulation agreement. Although several versions of Khalid's treaty were recorded in the early Muslim and Christian sources, they generally concur that the inhabitants' lives, properties and churches were to be safeguarded, in return for their payment of the
jizya (
poll tax). Imperial properties were confiscated by the Muslims. The treaty probably served as the model for the capitulation agreements made throughout Syria, as well Iraq and Egypt, during the early Muslim conquests. Although the accounts cited by
al-Waqidi (d. 823) and Ibn Ishaq agree that Damascus surrendered in August/September 635, they provide varying timelines of the siege ranging from four to fourteen months.
Battle of Yarmouk , in the vicinity of the Battle of Yarmouk In the spring of 636, Khalid withdrew his forces from Damascus to the old Ghassanid capital at
Jabiya in the
Golan. He was prompted by the approach of a large Byzantine army dispatched by Heraclius, consisting of imperial troops led by
Vahan and
Theodore Trithyrius and frontier troops, including Christian Arab light cavalry led by the Ghassanid
phylarch Jabala ibn al-Ayham and Armenian auxiliaries led by a certain Georgius (called Jaraja by the Arabs). The sizes of the forces are disputed by modern historians; Donner holds the Byzantines outnumbered the Muslims four to one,
Walter E. Kaegi writes the Byzantines "probably enjoyed numerical superiority" with 15,000–20,000 or more troops, and John Walter Jandora holds there was likely "near parity in numbers" between the two sides with the Muslims at 36,000 men (including 10,000 from Khalid's army) and the Byzantines at about 40,000. The Byzantine army set up camp at the
Ruqqad tributary west of the Muslims' positions at Jabiya. Khalid consequently withdrew, taking up position north of the
Yarmouk River, close to where the Ruqqad meets the Yarmouk. The area spanned high hilltops, water sources, critical routes connecting Damascus to the
Galilee and historic pastures of the Ghassanids. For over a month, the Muslims held the strategic high ground between
Adhri'at (modern
Daraa) and their camp near
Dayr Ayyub and bested the Byzantines in a skirmish outside Jabiya on 23 July 636. Jandora asserts that the Byzantines' Christian Arab and Armenian auxiliaries deserted or defected, but that the Byzantine force remained "formidable", consisting of a vanguard of
heavy cavalry and a rear guard of infantrymen when they approached the Muslim defensive lines. illustrator (). Khalid split his cavalry into two main groups, each positioned behind the Muslims' right and left infantry wings to protect his forces from a potential envelopment by the Byzantine heavy cavalry. He stationed an elite squadron of 200–300 horsemen to support the center of his defensive line and left archers posted in the Muslims' camp near Dayr Ayyub, where they could be most effective against an incoming Byzantine force. The Byzantines' initial assaults against the Muslims' right and left flanks successively failed, but they kept up the momentum until the entire Muslim line fell back or, as contemporary Christian sources maintain, feigned retreat. The Byzantines pursued the Muslims into their camp, where the Muslims had their camel herds hobbled to form a series of defensive perimeters from which the infantry could fight and which Byzantine cavalries could not easily penetrate. As a result, the Byzantines were left vulnerable to attack by Muslim archers, their momentum was halted and their left flank exposed. Khalid and his cavalries used the opportunity to pierce the Byzantines' left flank, taking advantage of the gap between the Byzantine infantry and cavalry. Khalid enveloped the opposing heavy cavalry on either side, but intentionally left an opening from which the Byzantines could only escape northward, far from their infantry. According to the 9th-century Byzantine historian
Theophanes, the Byzantine infantry mutinied under Vahan, possibly in light of Theodore's failure to counter the attack on the cavalry. The infantry was subsequently routed. The Byzantine cavalry, meanwhile, had withdrawn north to the area between the Ruqqad and
Allan tributaries. Khalid sent a force to pursue and prevent them from regrouping. He followed up with a nighttime operation in which he seized the Ruqqad bridge, the only viable withdrawal route for the Byzantines. The Muslims then assaulted the Byzantines' camps on 20 August and massacred most of the Byzantine troops, or induced panic in Byzantine ranks, causing thousands to die in the Yarmouk's ravines in an attempt to make a westward retreat. Jandora credits the Muslim victory at Yarmouk to the cohesion and "superior leadership" of the Muslim army, particularly the "ingenuity" of Khalid, in comparison to the widespread discord in the Byzantine army's ranks and the conventional tactics of Theodorus, which Khalid "correctly anticipated". In Gil's view, Khalid's withdrawal before the army of Heraclius, the evacuation of Damascus and the counter-movement on the Yarmouk tributaries "are evidence of his excellent organising ability and his skill at manoeuvring on the battlefield". The Byzantine rout marked the destruction of their last effective army in Syria, immediately securing earlier Muslim gains in Palestine and
Transjordan and paving the way for the recapture of Damascus in December, this time by Abu Ubayda, and the conquest of the
Beqaa Valley and ultimately the rest of Syria to the north. In Jandora's assessment, Yarmouk was one of "the most important battles of World History", ultimately leading to Muslim victories which expanded the
Caliphate between the
Pyrenees mountains and Central Asia.
Demotion Khalid was retained as supreme commander of the Muslim forces in Syria between six months and two years from the start of Umar's caliphate, depending on the source. Modern historians mostly agree that Umar's dismissal of Khalid probably occurred in the aftermath of Yarmouk. The caliph appointed Abu Ubayda to Khalid's place, reassigned his troops to the remaining Muslim commanders and subordinated Khalid under the command of one of Abu Ubayda's lieutenants; a later order deployed the bulk of Khalid's former troops to Iraq. Varied causes for Khalid's dismissal from the supreme command are cited by the early Islamic sources. Among them were his independent decision-making and minimal coordination with the leadership in Medina; older allegations of moral misconduct, including his execution of Malik ibn Nuwayra and subsequent marriage to Malik's widow; accusations of generous distribution of booty to members of the tribal nobility to the detriment of eligible early Muslim converts; personal animosity between Khalid and Umar; and Umar's uneasiness over Khalid's heroic reputation among the Muslims, which he feared could develop into a personality cult. The modern historians De Goeje,
William Muir and
Andreas Stratos viewed Umar's enmity with Khalid as a contributing cause of Khalid's dismissal. Shaban acknowledges the enmity but asserts it had no bearing on the caliph's decision. De Goeje dismisses Khalid's extravagant grants to the tribal nobility, a common practice among the early Muslim leaders including Muhammad, as a cause for his sacking. Muir, Becker, Stratos and
Philip K. Hitti have proposed that Khalid was ultimately dismissed because the Muslim gains in Syria in the aftermath of Yarmouk required the replacement of a military commander at the helm with a capable administrator such as Abu Ubayda. Athamina doubts all the aforementioned reasons, arguing the cause "must have been vital" at a time when large parts of Syria remained under Byzantine control and Heraclius had not abandoned the province. Athamina holds that "with all his military limitations", Abu Ubayda would not have been considered "a worthy replacement for Khālid's incomparable talents". Medina's lack of a regular standing army, the need to redeploy fighters to other fronts, and the Byzantine threat to Muslim gains in Syria all required the establishment of a defense structure based on the older-established Arab tribes in Syria, which had served as confederates of Byzantium. After Medina's entreaties to the leading confederates, the Ghassanids, were rebuffed, relations were established with the Kalb,
Judham and
Lakhm. These tribes likely considered the large numbers of outside Arab tribesmen in Khalid's army as a threat to their political and economic power. Khalid's initial force of 500–800 men had swelled to as high as 10,000 as a result of tribesmen joining his army's ranks from the Iraqi front or Arabia and as high as 30,000–40,000 factoring in their families. Athamina concludes Umar dismissed Khalid and recalled his troops from Syria as an overture to the Kalb and their allies.
Operations in northern Syria Abu Ubayda and Khalid proceeded from Damascus northward to
Homs (called Emesa by the Byzantines) and besieged the city probably in the winter of 636–637. The siege held amid a number of sorties by the Byzantine defenders and the city capitulated in the spring. Per the surrender terms, taxes were imposed on the inhabitants in return for guarantees of protection for their property, churches, water mills and the city walls. A quarter of the church of St. John was reserved for Muslim use, and abandoned houses and gardens were confiscated and distributed by Abu Ubayda or Khalid among the Muslim troops and their families. Owing to its proximity to the desert steppe, Homs was viewed as a favorable place of settlement for Arab tribesmen and became the first city in Syria to acquire a large Muslim population. Information about the subsequent conquests in northern Syria is scant and partly contradictory. Khalid was dispatched by Abu Ubayda to conquer
Qinnasrin (called Chalcis by the Byzantines) and nearby
Aleppo. Khalid
routed a Byzantine force led by a certain Minas in the outskirts of Qinnasrin. There, Khalid spared the inhabitants following their appeal and claim that they were Arabs forcibly conscripted by the Byzantines. He followed up by besieging the walled town of Qinnasrin, which capitulated in August/September 638. He and Iyad ibn Ghanm then launched the first Muslim raid into Byzantine
Anatolia. Khalid made Qinnasrin his headquarters, settling there with his wife. Khalid was appointed Abu Ubayda's deputy governor in Qinnasrin in 638. The campaigns against Homs and Qinnasrin resulted in the conquest of northwestern Syria and prompted Heraclius to abandon his headquarters at
Edessa for
Samosata in Anatolia and ultimately to the imperial capital of
Constantinople. Khalid may have participated in the
siege of Jerusalem, which capitulated in 637 or 638. According to al-Tabari, he was one of the witnesses of a
letter of assurance by Umar to Patriarch
Sophronius of Jerusalem guaranteeing the safety of the city's people and property.
Dismissal and death According to Sayf ibn Umar, later in 638 Khalid was rumored to have lavishly distributed war spoils from his northern Syrian campaigns, including a sum to the Kindite nobleman
al-Ash'ath ibn Qays. Umar consequently ordered that Abu Ubayda publicly interrogate and relieve Khalid from his post regardless of the interrogation's outcome, as well as to put Qinnasrin under Abu Ubayda's direct administration. Following his interrogation in Homs, Khalid issued successive farewell speeches to the troops in Qinnasrin and Homs before being summoned by Umar to Medina. Sayf's account notes that Umar sent notice to the Muslim garrisons in Syria and Iraq that Khalid was dismissed not as a result of improprieties but because the troops had become "captivated by illusions on account of him [Khalid]" and he feared they would disproportionately place their trust in him rather than God. Khalid's sacking did not elicit public backlash, possibly due to existing awareness in the Muslim polity of Umar's enmity toward Khalid, which prepared the public for his dismissal, or because of existing hostility toward the Makhzum in general as a result of their earlier opposition to Muhammad and the early Muslims. In the account of Ibn Asakir, Umar declared at a council of the Muslim army at Jabiya in 638 that Khalid was dismissed for lavishing war spoils on war heroes, tribal nobles and poets instead of reserving the sums for needy Muslims. No attending commanders voiced opposition, except for a Makhzumite who accused Umar of violating the military mandate given to Khalid by Muhammad. According to the Muslim jurist
al-Zuhri (d. 742), before his death in 639, Abu Ubayda appointed Khalid and Iyad ibn Ghanm as his successors, but Umar confirmed only Iyad as governor of the
Homs–Qinnasrin–Jazira district and appointed Yazid ibn Abi Sufyan governor over the rest of Syria, namely the districts of
Damascus,
Jordan and
Palestine. Following his dismissal, some sources report that Khalid spent his remaining years in Homs with his family, rarely leaving the city and largely withdrawn from public life, while remaining devoted to Islam. Khalid died in Medina or Homs in 21 AH (). Purported
hadiths related about Khalid include Muhammad's urgings to Muslims not to harm Khalid and prophecies that Khalid would be dealt injustices despite his tremendous contributions to Islam. In Islamic literary narratives, Umar expresses remorse over dismissing Khalid, and the women of Medina mourn his death en masse, with Umar later stating on his deathbed that had Abu Ubayda,
Muadh ibn Jabal, or Khalid been alive, he would have chosen one of them as his successor. Athamina considers these all to be "no more than latter-day expressions of sympathy on the part of subsequent generations for the heroic character of Khalid as portrayed by Islamic tradition". ==Legacy==