In August 636, over about six days near the Yarmouk River2 on the edge of Syria, the Arab army of the Rashidun Caliphate under Khalid ibn al-Walid destroyed the main Byzantine field army. Khalid's fast, well-led horsemen wore the larger Byzantine force down and, with a dust-laden wind that the Byzantine chronicler Theophanes says blew into the Byzantines' faces, broke it completely. The victory ended centuries of Roman rule in Syria and opened the Levant to the early Muslim conquests.
It is one of the most decisive battles that most people have never heard of. In six days on a dusty plateau above a river gorge, the eastern Roman Empire lost Syria, the Persian and Roman worlds began to give way to a new one, and the map of the Middle East was redrawn for centuries to come.
A new power out of Arabia
In the 630s the armies of the new Rashidun Caliphate burst out of Arabia into the lands of the two great empires of the age, Byzantine Rome and Sasanian Persia, both exhausted by a long war against each other. The Arabs had already taken Damascus, though they abandoned it again as the great Byzantine army advanced. Emperor Heraclius, directing the campaign from the north3, gathered a large army to drive them out of Syria for good.
Six days by the river
The two armies faced each other for days on the plateau above the Yarmouk, a river running through deep gorges that would trap a beaten army. The Byzantine force was larger and mixed, with Greek, Armenian and Arab Christian contingents; the Arab army was smaller but united and highly mobile. Its nominal commander was Abu Ubayda ibn al-Jarrah2, but the fighting was directed by Khalid ibn al-Walid, the ablest Arab general, who massed his cavalry into a mobile reserve he could throw wherever the line bent.
The storm and the rout
After days of attack and counterattack, the decisive blow came on the last day. By tradition a hot wind drove dust into the faces of the Byzantines4, and Khalid launched his massed horsemen against their flank and rear, cutting them off from their line of retreat. Pinned against the gorges, the great Byzantine army broke1 and was destroyed, many thousands killed in the rout and the ravines behind them.
Farewell to Syria
Yarmouk shattered Byzantine power in the Levant.3 Damascus and the other cities fell for good, Jerusalem surrendered within a few years2, and the empire pulled back behind the mountains of Anatolia. Tradition has the emperor Heraclius bidding a bitter farewell to Syria5 as he withdrew. The battle was one of the most consequential in history, opening the whole Near East to the astonishing early spread of Islam.