In 610, during the Byzantine–Sasanian War of 602–628, Heraclius became the emperor of the Byzantine Empire,[10] after overthrowing Phocas. Meanwhile, the Sasanian Empire conquered Mesopotamia and in 611 they overran Syria and entered Anatolia, occupying Caesarea Mazaca (now Kayseri, Turkey). In 612, Heraclius managed to expel the Persians from Anatolia but was decisively defeated in 613 when he launched a major offensive in Syria against the Persians.[11] Over the following decade, the Persians were able to conquer Palestine and Egypt. Meanwhile, Heraclius prepared for a counterattack and rebuilt his army.
In 622, Heraclius finally launched his offensive.[12] After his overwhelming victories over the Persians and their allies in the Caucasus and Armenia, Heraclius launched a winter offensive against the Persians in Mesopotamia in 627, winning a decisive victory at the Battle of Nineveh thus threatening the Persian capital city of Ctesiphon. Discredited by the series of disasters, Khosrow II was overthrown and killed in a coup led by his son Kavadh II,[13] who immediately sued for peace and agreed to withdraw from all occupied territories of the Byzantine Empire. Heraclius restored the True Cross to Jerusalem with a majestic ceremony in 629.
Meanwhile, there had been rapid political development in the Arabian Peninsula, where Muhammad had been preaching Islam and, by 630, had successfully annexed most of Arabia under a single political authority. When Muhammad died in June 632, Abu Bakr was chosen as caliph and his political successor. Troubles emerged soon after Abu Bakr's succession, and several Arab tribes openly revolted against Abu Bakr, who declared war against the rebels. In what became known as the Ridda wars of 632–633, Abu Bakr managed to defeat his opponents and unite Arabia under the central authority of the caliph at Medina.
Once the rebels had been subdued, Abu Bakr began a war of conquest, beginning with Iraq. Sending his most brilliant general, Khalid ibn al-Walid, Iraq was conquered in a series of successful campaigns against the Sassanid Persians. Abu Bakr's confidence grew, and once Khalid established his stronghold in Iraq, Abu Bakr issued a call to arms for the invasion of Syria in February 634.[16] The Muslim invasion of Syria was a series of carefully planned and well-co-ordinated military operations, which employed strategy, instead of pure strength, to deal with the Byzantine defensive measures.[17]
The Muslim armies, however, soon proved to be too small to handle the Byzantine response, and their commanders called for reinforcements. Khalid was sent by Abu Bakr from Iraq to Syria with reinforcements and to lead the invasion. In July 634, the Byzantines were decisively defeated at Ajnadayn. Damascus fell in September 634, followed by the Battle of Fahl in which the last significant garrison of Palestine was defeated and routed.
After Abu Bakr died in 634, his successor, Umar, was determined to continue the Caliphate's expansion deeper into Syria.Though previous campaigns led by Khalid had been successful, he was replaced by Abu Ubaidah. Having secured southern Palestine, Muslim forces now advanced up the trade route, and Tiberias and Baalbek fell without much struggle and conquered Emesa early in 636.
Having seized Emesa, the Muslims were just a march away from Aleppo, a Byzantine stronghold, and Antioch, where Heraclius resided. Seriously alarmed by the series of setbacks, Heraclius prepared for a counterattack to reacquire the lost regions.In 635 Yazdegerd III, the Emperor of Persia, sought an alliance with the Byzantine Emperor. Heraclius married off his daughter (according to traditions, his granddaughter) Manyanh to Yazdegerd III, to cement the alliance. While Heraclius prepared for a major offensive in the Levant, Yazdegerd was to mount a simultaneous counterattack in Iraq, in what was meant to be a well-coordinated effort. When Heraclius launched his offensive in May 636, Yazdegerd could not co-ordinate with the maneuver, probably owing to the exhausted condition of his government, and what would have been a decisive plan missed the mark.
Byzantine preparations began in late 635 and by May 636 Heraclius had a large force concentrated at Antioch in Northern Syria.[2The assembled Byzantine army contingents consisted of, Slavs, Franks, Georgians, Armenians and Christian Arabs.[The force was organized into five armies, the joint leader of which was Theodore Trithyrius. Vahan, an Armenian and the former garrison commander of Emesa,was made the overall field commander,and had under his command a purely Armenian army. Buccinator (Qanatir), a Slavic prince, commanded the Slavs and Jabalah ibn al-Aiham, king of the Ghassanid Arabs, commanded an exclusively Christian Arab force. The remaining contingents, all European, were placed under Gregory and Dairjan.Heraclius himself supervised the operation from Antioch. Byzantine sources mention Niketas, son of the Persian general Shahrbaraz, among the commanders, but it is not certain which army he commanded.
The Rashidun army was then split into four groups: one under Amr in Palestine, one under Shurahbil in Jordan, one under Yazid in the Damascus-Caesarea region and the last one under Abu Ubaidah along with Khalid at Emesa.
Muslim strategy
The Muslims discovered Heraclius' preparations at Shaizar through Roman prisoners. Alert to the possibility of being caught with separated forces, which could be destroyed, Khalid called for a council of war and advised Abu Ubaidah to pull the troops back from Palestine and Northern and Central Syria and then to concentrate the entire Rashidun army in one place.Abu Ubaidah ordered the concentration of troops in the vast plain near Jabiyah, as control of the area made cavalry charges possible and facilitated the arrival of reinforcements from Umar so that a strong, united force could be fielded against the Byzantine armies.The position also benefited from close proximity to the Rashidun stronghold of Najd, in case of retreat. Instructions were also issued to return the jizya (tribute) to the people who had paid it.
However, once concentrated at Jabiyah, the Muslims were subject to raids from pro-Byzantine Ghassanid forces. Encamping in the region was also precarious as a strong Byzantine force was garrisoned in Caeseara and could attack the Muslim rear while they were held in front by the Byzantine army. On Khalid's advice the Muslim forces retreated to Dara’ah (or Dara) and Dayr Ayyub, covering the gap between the Yarmouk Gorges and the Harra lava plains, and established a line of camps in the eastern part of the plain of Yarmouk. That was a strong defensive position, and the maneuvers pitted the Muslims and Byzantines into a decisive battle, which the latter had tried to avoid.During the maneuvers, there were no engagements except for a minor skirmish between Khalid's elite light cavalry and the Byzantine advance guard.
Evaluation
The Imperial Byzantine commanders allowed their enemy to have the battlefield of his choosing. Even then, they were at no substantial tactical disadvantage.Khalid knew all along that he was up against a force superior in numbers and, until the last day of the battle, conducted an essentially defensive campaign, suited to his relatively limited resources. When he decided to take the offensive and attack on the final day of battle, he did so with a degree of imagination, foresight and courage that none of the Byzantine commanders managed to display. Although he commanded a smaller force and needed all the men he could muster, he had the confidence and foresight to dispatch a cavalry regiment the night before his assault to seal off a critical path of the retreat that he had anticipated for the enemy army.
Because of his leadership at Yarmouk, Khalid ibn al-Walid is considered one of the finest generals in history,and his use of mounted warriors throughout the battle showed just how well he understood the potential strengths and weaknesses of his mounted troops. His mobile guard moved quickly from one point to another, always changed the course of events wherever they appeared, and, then just as quickly, galloped away to change the course of events elsewhere on the field.
Vahan and his Byzantine commanders did not manage to deal with the mounted force and use the sizable advantage of their army effectively.Their own Byzantine cavalry never played a significant role in the battle and were held in static reserve for most of the six days.They never pushed their attacks, and even when they obtained what could have been a decisive breakthrough on the fourth day, they were unable to exploit it. There appeared to be a decided lack of resolve among the Imperial commanders, but that may have been caused by difficulties commanding the army because of internal conflict. Moreover, many of the Arab auxiliaries were mere levies, but the Muslim Arab army consisted for a much larger part of veteran troops.
The original strategy of Heraclius, to destroy the Muslim troops in Syria, needed a rapid and quick deployment, but the commanders on the ground never displayed those qualities. Ironically, on the field at Yarmouk, Khalid carried out, on a small tactical scale, what Heraclius had planned on a grand strategic scale. By rapidly deploying and manoeuvering his forces, Khalid was able to concentrate sufficient forces at specific locations on the field temporarily to defeat the larger Byzantine army in detail. Vahan was never able to make his numerical superiority count, perhaps because of the terrain, which prevented large-scale deployment.
However, Vahan never attempted to concentrate a superior force to achieve a critical breakthrough.Although he was on the offensive five out of the six days, his battle line remained remarkably static. That stands in stark contrast to the very successful offensive plan, which Khalid carried out on the final by reorganising virtually all his cavalry and committing it to a grand manoeuvre, which won the battle.
