"Si vis pacem, para bellum"

– Publius Flavius Vegeitus

Prologue: Yarmouk

In the early months of the year 636, an army mounted on camels crossed the Syrian border and – in what appeared to be a suicidal attack – invaded the Eastern Roman Empire. This state, better known as Byzantium, was the glittering, cultured bulwark of Christendom, whose borders stretched from the Atlantic coast of southern Spain in the west, to the deserts of modern Saudi Arabia in the east.¹ On every side, the empire seemed ascendant. After four centuries of intermittent war, Rome’s ancient enemy Persia had finally been defeated, decisively smashed by the brilliant Roman soldier-emperor Heraclius. 

Byzantine chroniclers were quick to anoint his reign as the new golden age. The ageing emperor was hailed as a new Moses leading his people out of the bondage of fear, a new Alexander the Great destroying the Persian threat, and a new Scipio Africanus vanquishing a modern Hannibal and restoring the glory of Rome. Once again, the Pax Romana had spread out over the war-torn lands of the Mediterranean. 

The invaders, on the other hand, were from the desert wastes of Arabia, a region outside the borders of the civilized world populated by squabbling, insignificant tribes. Aside from a few raids into imperial territory, the people of this arid land had played no important part in human history and gave no sign that they ever would. In 622, however, a charismatic camel-driver's son named Muhammed declared that he was God's final prophet, come to purify the corrupted message of Judaism and Christianity.² 

Muhammed was no simple crackpot or fleeting strongman. He preached absolute obedience and submission (Islam) to God's will, and combined it with a political and military system that made Islam more than just a religion.³ He inspired the quarreling tribes of Arabia with the vision of a world divided between those who had submitted to Islam – Dar al-Islam, the 'House of Islam' – and those who had yet to be conquered – Dar al-Harb, the 'House of War'. The vast energies of the Arabs, instead of dissipating in internecine feuds, were focused on expanding the House of Islam at the point of the sword. 

The success of this first great wave of jihad, or holy war, was breathtaking. Within a decade Muslim armies had conquered most of Arabia, and although Muhammed died of a fever in Mecca in 632, a series of equally aggressive successors continued the advance.⁴ As early as 634 raiding parties entered imperial territory before arriving in strength two years later. Their timing couldn't have been better.

Despite its glittering appearance, Byzantine power was a mirage. The last two decades of its most recent war had cost the empire more than two hundred thousand casualties, and had left it vulnerable and exhausted. Religious divisions wracked the southeastern provinces, and the emperor’s attempt to root out heretical opinions by force only exacerbated them. The empire desperately needed leadership, but by 636, the conquering hero, Heraclius, was a shell of himself, with stooped shoulders and trembling hands. Worn out by a quarter of a century on the throne, he was showing signs of mental instability and had begun to suffer from the violent spasms that were soon to kill him. 

The emperor may not have understood the enemy he was facing – like most Byzantines he assumed they were a new Christian heresy or a Jewish sect – but he at least recognized a threat and raised an army eighty thousand strong to defend the empire. Too ill to personally lead it, he set up a command center in Antioch, the second greatest metropolis in the empire, and sent the army under the command of a collection of generals into neighboring Syria where the Islamic force waited. 

The two armies met on a sandy plain near the Yarmouk, one of the tributaries of the Jordan River. It was an inhospitable spot, an upland region on the frontier between the modern nations of Israel, Jordan, and Syria, just southeast of the contested Golan Heights. In the seventh century it was an even more remote place, flanked by impassable deserts, and scorched hills, hardly the place for one of history's most decisive battles to be fought. 

The Byzantine force was easily superior – at least numerically – but now within sight of their enemy, they sat paralyzed. For five days they sent out tentative scouting raids, keeping careful watch, but refusing to engage. While they dithered, Muslim reinforcements poured in, strengthening the Islamic force and demoralizing the Christian one.⁵ 

It was the Muslim army that acted first. On the morning of August 20, 636, under cover of a blinding sandstorm that was blowing in the faces of their enemies, the Arabs charged. At first the Imperial army stood their ground, but in the thick of the fighting twelve thousand of their Christian Arab allies – whose pay was seriously in arrears – switched sides, and the imperial army broke. Panicked, surrounded, and confused, they stood little chance. Most were butchered as they attempted to scramble to safety. 

In Antioch, news of the disaster shattered what was left of Heraclius' deteriorating mind. He had risked everything on this battle and lost. Believing that he had been abandoned by God, he made no further attempt to check the Islamic advance.⁶ The only interruption he made in his retreat to Constantinople was a brief stop in the Holy City of Jerusalem. 

Just six years earlier he had entered the city in triumph, carrying the empire's holiest relic – the True Cross – on his back. Dressed as a simple penitent, he had walked barefoot up the Via Dolorosa, the 'Way of Sorrow' that Christ had taken to his crucifixion. The path ended at the Church of the Holy Sepulcher, the magnificent basilica that Constantine the Great had built, and there Heraclius had hung his prize above the high altar. It had been the highlight of his reign, unassailable evidence of God's favor.

Now, a broken and pathetic figure, Heraclius once again entered the church. Few watching would have missed the symbolism as the stricken monarch carefully pulled down the True Cross and loaded it on a ship along with most of the city's other relics. Weeping openly, he departed, leaving the Christian east to its fate. 

Deprived of leadership and unable to comprehend this new aggressor, the empire crumbled with astonishing speed. The Roman Middle East – which had been Christian for more than three centuries – had effectively received its deathblow. Less than a year after the battle, the Caliph entered Jerusalem in person, wresting the city from Christian hands. Within twelve months, Damascus had fallen along with the rest of Syria and present-day Israel, and Jordan. Within a decade both Egypt and Armenia had fallen; within two, Iraq and most of Iran were gone. Less than a century after Yarmouk, Islamic armies had taken North Africa and Spain, and were within a hundred and fifty miles of Paris. Three quarters of the Christian world was gone, and most devastatingly of all, Christianity had been evicted from the land of its birth. 

The mood was summed up by the Patriarch of Jerusalem, who had turned over the city to its new masters to avoid further bloodshed. As he watched the Caliph, mounted on a snow white camel, moving to take possession of the Temple Mount, he whispered, "Behold, the abomination of desolation..." It was a sign – as Christ himself had warned – that the end of the world was at hand.⁷