Decline of Byzantine Empire and Rise of Islam. Are the two connected?

From The Lecture Series: The Roman Empire: From Augustus to the Fall of Rome

By Gregory S. Aldrete, Ph.D., University of Wisconsin-Green Bay

In the 7th Century, the Byzantine Empire was at the height of its power in many ways. But this period also witnessed the emergence of a new force, a wave that would sweep over the Byzantine Empire and leave behind a permanent imprint. How did Islam impact the Byzantine Empire, and was this impact greater than the one inflicted by the longstanding rival of the Eastern Roman Empire—the Sassanian Empire? Let’s find out.

A fresco depicting the war between Heraclius and Khosroe II, in which men with swords and shields in hand, men on horses,   and even men completely covered in armor and battling it out.
The Byzantine Empire achieved one of its greatest triumphs when Emperor Heraclius defeated their longstanding rival, the Sassanian Empire, in a war that lasted almost 20 years. (Image: Piero della Francesca/Public domain)

Soon after Emperor Justinian, another key figure in Byzantine history came to the fore. In the early 7th century, the reign of Emperor Heraclius began. He was a general who rebelled against the then current emperor, Phocas, and deposed him.

Byzantine Empire Vs. Sassanian Empire

Heraclius led the Byzantine Empire to one of its greatest triumphs over its longstanding Persian rival—the Sassanian Empire. Heraclius was a gifted general and led a vigorous series of campaigns against the Sassanians, who themselves were governed at the time by a particularly able and aggressive king, Khosrow II.

The war between these two men lasted almost 20 years, and included a number of spectacular successes and disasters on both sides. Khosrow II began by capturing much of Byzantium’s eastern territories, and at one point, in alliance with the Avars, even besieged Constantinople itself.

Heraclius directed a series of counterattacks, and unusually, often fought in the front rank alongside his soldiers. This was risky behavior, but it earned him the respect and admiration of his troops.

One of Heraclius’s greatest victories took place in December 627 A.D., when he invaded the Sassanian heartland and thoroughly smashed their main army at the Battle of Nineveh, located in modern Iraq.

In this climactic battle of the long war, Heraclius allegedly personally slew several foes, suffering a wound to his face in return. Khosrow was not present at this battle, but with his army destroyed, his power was compromised and he was assassinated two months later.

Heraclius acquired a considerable war bounty, supposedly including the fragments of the True Cross, which had been seized by Khosrow when he had earlier captured Jerusalem. This holy relic was borne in triumph back to Constantinople.

This is a transcript from the video series The Roman Empire: From Augustus to the Fall of Rome. Watch it now, on The Great Courses Plus.

The Founding and Rise of Islam

If Heraclius had died ,then, he probably would have gone down in history as one of the greatest Roman emperors. However, it was his misfortune to live longer and witness the loss of much of his empire to a new and apparently irresistible force.

While the Byzantines and Sassanians were bleeding each other dry over the course of their prolonged and bitter struggle, a new power had emerged from one of the most obscure corners of the Mediterranean that, in a remarkably short period of time, would explode onto the scene and sweep away much of the previous world order.

In 610 A.D., a middle-aged merchant in the town of Mecca on the Arabian Peninsula began to experience visions in which the angel Gabriel appeared to him, imparted to him a series of revelations from God, and commanded him to recite them back. This man, of course, was Mohammed, the collected lessons became known as the Qur’an—literally, ‘the Recitations’—and the religion that he founded was Islam.

An illustration of a man wearing a white turban-like headgear, sporting long black hair and long black beard, and wearing   a white robe receiving a message from an angel with exquisitely designed wings, wearing a golden crown and wearing a long   flowing dress.
In 610 A.D., a middle-aged merchant named Mohammed in the town of Mecca on the Arabian Peninsula began to experience visions in which the angel Gabriel appeared to him and imparted to him a series of revelations from God, and commanded him to recite them back. These collected lessons came to be known as the Qur’an, and the religion that he founded was Islam. (Image: Unknown author/Public domain)

The religion established by Mohammed advocated a stark form of monotheism in which the primacy of God as the one and only deity was stressed, and nothing was allowed to come between God and the worshipper. Acknowledgment of God’s omnipotence and submitting oneself to his will were all-important; this concept is reflected in the word ‘Islam’, which can be translated as ‘submission’.

Mohammed identified God or, in Arabic, Allah, as the same God who was revered by the Jews and the Christians. And in Islam, figures such as Abraham, Moses, and Jesus are venerated as human prophets who had received earlier divine revelations.

Mohammed, then, was believed to be the last in this line of prophets, and had been granted the fullest and most accurate version of God’s message.

Mohammed gathered around him a group from Mecca of converts to the new religion, but the people among whom Islam really took hold were the hardy nomadic Arab tribes of the surrounding desert.

By the time of Mohammed’s death in 632 A.D., Islam had spread throughout these tribes, and over the next 30 years, under the leadership of Mohammed’s four caliphs, or ‘successors’, these tribes erupted into the Mediterranean world and conquered vast territories. Mounted on swift-moving camels, these raiders rolled irresistibly over their opponents.

Learn more about when and why the Roman Empire fell.

Decline of Byzantine Empire

The long Byzantine-Sassanian wars had exhausted both sides, and left these once-powerful empires vulnerable. Heraclius fought gamely, but was unable to stem the tide, and had to endure watching one section of his empire lost after another.

In 636 A.D., at the Battle of Yarmouk, the Byzantine Army was decisively defeated, and in the very same year, the Sassanians were crushed at the Battle of al-Qadisiyyah, leaving the entire East open to invasion and conquest by the Arabs.

In 636 A.D., Byzantium lost Jerusalem, the most sacred city in Christendom, and soon after, the entire Sassanian Empire crumbled and was brushed aside by the newcomers. Egypt fell in 642 A.D., and the southern Mediterranean coast, encompassing what is today Libya and Tunisia, soon followed.

The Byzantine Empire still held Constantinople and sections of the Balkans and Anatolia, and this much-reduced version of the empire would manage to continue for another 800 years.

Heraclius lived to witness most of these losses, finally dying in 641 A.D. This great wave of subjugation finally subsided in the mid-8th century, by which time, in the West, the remainder of North Africa and Spain had been subdued, and in the East, the Islamic armies had reached the borders of India.

The Arabic conquests fundamentally reshaped the Mediterranean world and created religious, cultural, and linguistic boundaries that persist even today.

Learn more about the Byzantine Empire.

Common Questions about the Decline of the Byzantine Empire and Rise of Islam

Q: What did Heraclius do?

Heraclius led the Byzantine Empire to one of its greatest triumphs over its longstanding Persian rival, the Sassanian Empire.

Q: What was the result of the Battle of Nineveh?

One of Heraclius’s greatest victories took place in December 627 A.D., when he invaded the Sassanian heartland and thoroughly smashed their main army at the Battle of Nineveh, located in modern Iraq.

Q: What is Prophet Mohammed’s story?

In 610 A.D., a middle-aged merchant named Mohammed in the town of Mecca on the Arabian Peninsula began to experience visions in which the angel Gabriel appeared to him, imparted to him a series of revelations from God, and commanded him to recite them back. The collected lessons became known as the Qur’an and the religion that he founded was Islam.

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