The Byzantine Empire, also known as the Eastern Roman Empire, spanned over a thousand years from the 4th to 15th century CE. At its height, it controlled large swaths of territory in Europe, North Africa, and the Middle East.
If you’re short on time, here’s a quick answer: After 330 CE, the Byzantine Empire gained control over much of the Balkans, Anatolia, the Levant, Egypt and North Africa at its peak. However it would lose territory later on to the Islamic conquests, Bulgarian Empire, loss of Italy and Sicily to Germanic tribes.
The Empire would continue losing territory until the Fall of Constantinople in 1453.
In this comprehensive article, we will analyze the ebb and flow of Byzantine territorial control – what new lands they gained influence over starting in 330 CE under Emperor Constantine, as well as territories they eventually lost control of amidst rising powers in Europe and the Middle East.
Territorial Gains up to Justinian I Reign
Conquests under Emperor Constantine
The Byzantine Empire greatly expanded its territories in the early 4th century under Emperor Constantine the Great. After winning control of the western provinces from his rival emperors, Constantine was able to conquer many new lands.
Some of Constantine’s major territorial gains included:<
- Conquering the Balkans – Constantine defeated Licinius to bring Serbia, Bulgaria and Greece under Byzantine control.
- Reconquering land in Anatolia – He drove the Goths out of this region in central modern-day Turkey.
- Taking over the province of Dacia – This area is now modern Romania and Moldova.
By 324 CE, Constantine had reunited much of the Roman Empire under his rule from the new Byzantine capital of Constantinople. His military victories greatly expanded the empire’s borders into southeastern Europe.
Additional Gains in the Balkans
In the late 4th and early 5th centuries, the Byzantines continued to make progress in conquering the Balkans. Emperors like Theodosius I campaigned extensively in the region.
Key conquests included:
- Taking most of Illyricum from Germanic tribes
- Defeating the Visigoths to regain territory in Greece
- Conquering Pannonia (modern Hungary) from the Huns
By the early 5th century, the Byzantine Empire controlled almost the entire Balkan peninsula south of the Danube River. These gains provided a strategic buffer against barbarian invasions from central Europe.
Reconquest of Africa and Italy
The Byzantines also managed to recover much of the lost Roman territory in North Africa and Italy during the 5th century.
Some highlights include:
- Reconquering the Roman province of Africa from the Vandals in 533-534 CE under Emperor Justinian I.
- Destroying the Ostrogothic Kingdom to regain control of Italy from 535-554 CE, also under Justinian.
According to historian J.B. Bury’s History of the Later Roman Empire, the Byzantine Empire reached its greatest extent by 555 CE, controlling an area of over 1 million square miles.
Justinian’s ambitious military campaigns reversed centuries of territorial losses and restored imperial control over much of the former Western Roman Empire.
Height of Byzantine Territorial Control
Conquests under Justinian I
The emperor Justinian I, who reigned from 527 to 565 CE, oversaw a dramatic expansion of the Byzantine Empire’s territory. Through a series of military campaigns, Justinian was able to reconquer many former Roman territories that had been lost in previous centuries.
Justinian’s most famous general was Belisarius, who led successful campaigns against the Vandals in North Africa and the Ostrogoths in Italy. In 533-534 CE, Belisarius defeated the Vandals and claimed North Africa for the Byzantine Empire.
This was an important victory, as it regained control over the valuable wheat-producing lands of North Africa.
In 535 CE, Belisarius invaded the Italian peninsula and quickly took Sicily and southern Italy from the Ostrogothic kingdom. After a long siege, Rome itself was retaken in 536 CE. The Ostrogoths continued to resist throughout Italy, but after several years of warfare, Belisarius and other Byzantine generals were able to drive them out completely by 553 CE.
These conquests reunited the core former Roman territories around the Mediterranean under Byzantine control. Other smaller campaigns further expanded the empire’s borders into Armenia, northern Africa, and parts of Spain.
Extent of Empire at Justinian’s Death
By the time Justinian died in 565 CE, the Byzantine Empire encompassed territory that Justinian proudly referred to as “Romania” – essentially a recreation of the eastern half of the Roman Empire at its height in the 2nd century CE.
The Byzantine Empire now controlled the Balkan Peninsula, Asia Minor, Syria, Armenia, North Africa, Italy, Sicily, and parts of Spain. The borders stretched approximately 2,000 miles from east to west and 900 miles from north to south.
It was by far the largest and most powerful state in Europe and the Mediterranean region.
However, Justinian’s ambitious conquests also overextended the empire’s resources. Many territories were regained only after years of warfare and were devastated in the process. Ongoing defense of these borders would prove costly for the empire in the coming centuries.
Nonetheless, the scale of Justinian’s reconquests represents the zenith of the Byzantine Empire’s power and territorial reach. Though it would cede some territories in later periods, the empire’s extensive borders at the time of Justinian’s death show how successfully it had managed to reclaim substantial portions of the old Roman Empire in the east.
Subsequent Territorial Losses and Decline
Loss of Levant and Egypt to Islamic Conquests
The Byzantine Empire suffered major territorial losses to the rapid expansion of Islam in the 7th and 8th centuries. Muslim forces conquered the wealthy provinces of Syria, Palestine, and Egypt, costing the empire over half of its population and agricultural production.
This dealt a devastating economic blow from which the empire never fully recovered.
Syria was the first territory to fall starting with the decisive defeat of Byzantine forces at the Battle of Yarmouk in 636 CE. The capital Damascus surrendered soon after. Over the next decade, Muslim armies continued advancing north seizing Antioch, Jerusalem, Caesarea, and Aleppo.
By 661 CE, the Byzantine Empire had lost the entire Levant region to the Rashidun and later Umayyad Caliphates.
Shortly after, Egypt was conquered between 639-642 CE ending nearly 1,000 years of Greco-Roman rule. The loss of the valuable North African province severed vital grain supplies to Constantinople causing food shortages.
It also surrendered tax revenues and strategic access to Mediterranean trade networks.
Loses in Sicily and Southern Italy
While the Byzantine Empire reclaimed some territories in the 10th century under military reforms, further losses of land occurred in Italy by the Norman adventurers. The wealthy theme of Sicily had been controlled by Byzantines for over 300 years before the ambitious Normans seized the island by 1091.
They continued their conquests in southern Italy which had long been a Byzantine battlefield against German emperors. By 1130, only small portions remained from the once formidable Byzantine holdings in Magna Graecia.
The Norman Kingdom of Sicily became Imperial rivals dominating trade networks in the Mediterranean.
Loss of Asia Minor and Balkans
The Crusades brought ruinous consequences to Byzantine borders from the 12th to 15th century. Constantinople never regained Anatolia after the shattering defeat by Seljuk Turks at the Battle of Manzikert in 1071.
This crippled Byzantine defenses leaving them unable to halt invading Ghaznavids and later Ottoman forces seizing land in Asia Minor.
In the Balkans, Frankish knights passed through Constantinople on the way to Holy Land crusades. Instead of defending Byzantine lands, many rogue crusaders raided and attacked territories around Greece and Thrace. This further weakened central Byzantine authority in the region.
By the 15th century, the Ottoman Empire had reduced Byzantine control to only Constantinople and a few ports in Greece. When Sultan Mehmed II captured the Byzantine capital in 1453, the mighty Eastern Roman Empire which had lasted over a millennium was finally extinguished.
In summary, the Byzantine Empire gained great territorial control after 330 CE under Constantine and Justinian, but eventually lost territory amid Islamic conquests, pressure from European powers, and internal decline.
At its height it controlled lands across 3 continents, only to dwindle down to Constantinople and small surrounds by the Empire’s end.