What If the Byzantine Empire Reconquered the Western Mediterranean?

The Actual History

In the 6th century CE, the Eastern Roman Empire (today commonly known as the Byzantine Empire) embarked on an ambitious campaign to reconquer the Western Mediterranean territories that had fallen to Germanic kingdoms in the previous century. This effort, known as the Justinianic Reconquest, was spearheaded by Emperor Justinian I (reigned 527-565 CE), who dreamed of restoring the Roman Empire to its former glory.

When Justinian ascended to the throne in 527 CE, the Western Roman Empire had effectively ceased to exist for over fifty years. The last Western Roman Emperor, Romulus Augustulus, had been deposed in 476 CE by the Germanic warlord Odoacer. By the early 6th century, the former Western provinces were divided among several Germanic kingdoms: the Ostrogoths ruled Italy and Sicily; the Vandals controlled North Africa, Sardinia, Corsica, and the Balearic Islands; the Visigoths dominated Spain and parts of southern Gaul (France); while various Frankish kingdoms had established control over most of Gaul.

The Eastern Roman Empire, meanwhile, had survived and even prospered, with its capital at Constantinople (modern Istanbul). Though it had lost some territories to the Sassanid Persian Empire in the east and faced ongoing threats from various peoples along the Danube frontier, the Eastern Empire remained wealthy, urbanized, and militarily formidable. Justinian, an ambitious ruler with a grand vision, saw an opportunity to reclaim the lost western territories and reunite the Roman world.

The reconquest began in 533 CE with an expedition against the Vandal Kingdom in North Africa. Justinian entrusted this campaign to his brilliant general Belisarius, who had already proven his worth by suppressing the Nika Riots in Constantinople (532 CE) and securing victories against the Persians. With a relatively small force of about 15,000 men, Belisarius achieved a stunning victory, defeating the Vandals at the Battle of Ad Decimum and capturing their capital, Carthage. By 534 CE, the entire Vandal Kingdom had been incorporated into the Eastern Roman Empire.

Encouraged by this success, Justinian turned his attention to Italy, which had been ruled by the Ostrogothic Kingdom since Theodoric the Great overthrew Odoacer in 493 CE. The campaign began in 535 CE, again led by Belisarius, who quickly secured Sicily and then moved into mainland Italy. By 540 CE, Belisarius had captured the Ostrogothic capital of Ravenna and taken King Vitiges as a prisoner to Constantinople.

However, the Gothic War in Italy proved far more protracted and difficult than the North African campaign. After Belisarius's departure, the Ostrogoths rallied under a new leader, Totila, who recaptured much of Italy. Belisarius was sent back but with inadequate resources. The war dragged on until another Byzantine general, Narses, finally defeated Totila in 552 CE at the Battle of Taginae. By 554 CE, the Byzantine Empire had established control over Italy, though at a tremendous cost in lives and resources.

Simultaneously, Byzantine forces had also secured parts of southern Spain from the Visigoths, beginning in 552 CE. This area, known as Spania, included important cities like Cartagena and Málaga, giving the Byzantines control of key Mediterranean ports.

At its greatest extent under Justinian, the reconquered territories included North Africa, Italy, Sicily, Sardinia, Corsica, the Balearic Islands, and southeastern Spain. This represented a significant restoration of Roman control over the Mediterranean, which Justinian's court historian Procopius proudly called "Mare Nostrum" (Our Sea) once again.

However, Justinian's reconquest proved ephemeral for several reasons:

Overextension: The campaigns stretched Byzantine military and financial resources to their limits, especially as the empire simultaneously faced threats from Persians in the east and Slavs and Avars in the Balkans.
Devastation: The protracted Gothic War left Italy economically ruined and depopulated. Rome itself changed hands multiple times and saw its population plummet from hundreds of thousands to perhaps tens of thousands.
Plague: The Justinianic Plague, a pandemic of what was likely bubonic plague, struck the Mediterranean world beginning in 541 CE, killing millions and undermining both the economy and military manpower.
Local Resistance: The Byzantine administration faced ongoing resistance in the reconquered territories, where the local population had adapted to Germanic rule and often viewed the Eastern Romans as foreign oppressors rather than liberators.
New Invasions: Shortly after Justinian's death, new threats emerged. The Lombards invaded Italy in 568 CE and quickly conquered much of the peninsula, reducing Byzantine holdings to Ravenna, Rome, Naples, and the far south. In Spain, the Visigoths gradually pushed back Byzantine forces. In the east, a renewed Persian threat forced the Byzantines to prioritize their eastern frontier.

By the early 7th century, much of Justinian's reconquest had been lost. The rise of Islam in the 630s CE and the subsequent Arab conquests further reduced Byzantine territory, with North Africa falling to Arab forces by the end of the 7th century. Byzantine control in Italy continued to shrink, though the empire maintained a foothold in southern Italy until the 11th century.

Justinian's reconquest, while impressive in its initial success, ultimately proved unsustainable. It represented the last serious attempt to reunite the Mediterranean basin under Roman rule. The resources expended on these campaigns may have fatally weakened the Byzantine Empire's ability to face subsequent challenges, particularly the rise of Islam. Nevertheless, the reconquest did extend the life of Roman institutions in the Western Mediterranean by several decades and helped transmit aspects of Roman law, administration, and culture that would influence medieval Europe.

The Point of Divergence

In this alternate timeline, the Byzantine reconquest of the Western Mediterranean unfolds more successfully and, crucially, proves more durable than in our history. The point of divergence occurs in the late 530s CE, during the critical phase of Justinian's campaigns.

Several key factors combine to create this alternate outcome:

First, let's imagine that the Justinianic Plague, which historically struck in 541 CE with devastating consequences, is significantly less severe in this timeline. Perhaps a slight mutation in the pathogen makes it less virulent, or different weather patterns affect the spread of the disease-carrying fleas. While some outbreaks still occur, they remain localized rather than becoming the catastrophic pandemic that historically killed millions across the Mediterranean world. This preserves Byzantine military manpower, tax revenue, and administrative capacity at a crucial moment.

Second, Justinian makes a critical strategic decision differently. In our timeline, after Belisarius captured Ravenna and the Ostrogothic king Vitiges in 540 CE, Justinian recalled his successful general due to a combination of court jealousy and the need to address a Persian invasion in the east. In this alternate timeline, Justinian instead gives Belisarius the reinforcements and authority needed to complete the pacification of Italy before the Ostrogoths can regroup under Totila. By 542 CE, all of Italy is securely under Byzantine control, with minimal devastation compared to the protracted historical conflict that dragged on until 554 CE.

Third, with Italy secured more quickly and efficiently, and with greater resources preserved due to the reduced impact of the plague, Justinian is able to commit more forces to the Iberian campaign. Rather than the limited coastal holdings of historical Spania, Byzantine forces secure most of southern and eastern Spain from the Visigoths by 550 CE, including the wealthy province of Baetica (modern Andalusia).

Fourth, Justinian implements more effective administrative policies in the reconquered territories. Rather than imposing heavy taxation immediately to recoup the costs of the campaigns, he grants tax exemptions for several years to allow economic recovery. He also shows greater cultural sensitivity, respecting local customs and incorporating Germanic nobles who are willing to accept imperial authority into the provincial administration, creating stakeholders in Byzantine rule rather than persistent opponents.

Finally, and perhaps most importantly, Justinian focuses on establishing a sustainable defensive system for the reconquered territories. He establishes a series of semi-autonomous military provinces (exarchates and themes) with locally recruited forces supplemented by Eastern Roman troops. These are supported by a revitalized naval presence in the Western Mediterranean, with new fleet bases at Carthage, Syracuse, Ravenna, and Cartagena.

By the time of Justinian's death in 565 CE, the Byzantine Empire in this timeline controls all of North Africa, Egypt, the Levant, Asia Minor, the Balkans, Italy, Sicily, Sardinia, Corsica, the Balearic Islands, and southern Spain—effectively reuniting the Mediterranean basin under Roman rule for the first time since the 5th century. More importantly, this reconstituted empire is administratively coherent, economically viable, and militarily defensible in ways that the overextended historical reconquest was not.

This alternate Byzantine Empire is poised to face the challenges of the coming centuries—including the rise of Islam—from a position of much greater strength, fundamentally altering the course of Mediterranean and European history.

Immediate Aftermath

Stabilization and Integration of Reconquered Territories

The decades following Justinian's more successful reconquest see a gradual stabilization and integration of the Western territories:

Administrative Reorganization: Justinian establishes three major administrative units in the West: the Exarchate of Africa (encompassing North Africa and the islands), the Exarchate of Italy (including the Italian peninsula and Dalmatia), and the Exarchate of Hispania (covering Byzantine holdings in the Iberian Peninsula). Each is governed by an exarch with both civil and military authority, allowing for more responsive governance than the historical separation of powers.
Pragmatic Religious Policy: While officially promoting Chalcedonian Christianity (Orthodox), Justinian adopts a more pragmatic approach toward Arian Christians (predominant among the Germanic population) and Monophysites in Egypt and Syria than in our timeline. This reduces religious tensions and facilitates integration of diverse populations into the imperial system.
Economic Recovery: With less devastation from warfare and plague, the Western Mediterranean experiences faster economic recovery. Trade networks reactivate, urban populations stabilize, and agricultural production increases. The gold solidus circulates as a common currency throughout the Mediterranean, facilitating commercial integration.

Military Restructuring

The Byzantine military undergoes significant adaptation to maintain control of the expanded empire:

Theme System Development: An early version of the theme system (military provinces where soldiers receive land in exchange for hereditary military service) is implemented in vulnerable frontier regions, particularly in northern Italy and southern Spain. This creates a self-sustaining defensive capability with troops personally invested in protecting their territories.
Naval Dominance: The Byzantine navy establishes uncontested control of the Mediterranean, with major fleet bases strategically positioned throughout the sea. This naval supremacy secures maritime trade routes, enables rapid military response to coastal threats, and projects imperial power.
Frontier Fortifications: Extensive fortification programs strengthen vulnerable land frontiers, particularly the northern Italian Alpine passes against potential Frankish or Lombard incursions, and the Spanish frontier against the Visigoths. These defenses are manned by local troops supplemented by regular army units.

Cultural and Religious Developments

The successful reconquest creates new patterns of cultural exchange and religious evolution:

Latin-Greek Bilingualism: With sustained Byzantine presence in the West, bilingualism becomes more common among elites. Latin remains the administrative language in the Western exarchates, while Greek predominates in the East, but knowledge of both languages spreads among officials, clergy, and merchants who move between regions.
Architectural Renaissance: Justinian's building program extends more successfully to the Western territories. New churches, fortifications, and public works constructed in the distinctive Byzantine style appear across North Africa, Italy, and Spain, physically embodying the imperial restoration.
Ecclesiastical Integration: The Western church remains more closely integrated with Constantinople than in our timeline. While the Bishop of Rome (Pope) maintains special prestige, his practical autonomy is more limited, as regular communication and oversight from Constantinople continues.

Diplomatic Realignment

The reconstituted empire forces surrounding powers to recalibrate their relationships with Byzantium:

Frankish Accommodation: The Frankish kingdoms in Gaul, facing a much stronger Byzantine presence on their southern borders, pursue diplomatic accommodation rather than expansion into Italy. Marriage alliances and trade agreements develop, with some Frankish nobles receiving Byzantine titles and honors.
Visigothic Containment: Confined to central and northern Spain, the Visigothic kingdom focuses on internal consolidation and gradual conversion from Arianism to Chalcedonian Christianity, partly to improve relations with their powerful Byzantine neighbor.
Persian Strategic Dilemma: The Sassanid Persian Empire, Byzantium's eastern rival, faces a more formidable opponent. This leads to a longer period of uneasy peace following the "Eternal Peace" treaty of 532 CE, as the Persians recognize that Byzantium can now bring greater resources to bear in any conflict.

Intellectual and Legal Continuity

The more successful reconquest enhances the preservation and transmission of classical knowledge:

Legal Harmonization: Justinian's legal reforms, particularly the Corpus Juris Civilis (Body of Civil Law), are implemented more effectively throughout the reunited empire. This creates greater legal continuity across the Mediterranean world and preserves Roman legal concepts more thoroughly in the West.
Educational Institutions: Schools and libraries in Western cities receive imperial patronage, slowing the decline of classical education. Centers of learning in Carthage, Rome, and Ravenna maintain higher levels of activity, preserving Greek and Latin literary traditions.
Technological Transfer: Byzantine technological knowledge in areas such as architecture, engineering, and agriculture spreads more effectively to the Western territories, helping to maintain higher levels of material civilization than occurred historically.

Long-term Impact

Political and Territorial Evolution

The reconstituted Byzantine Empire follows a significantly different trajectory over the following centuries:

Response to Islamic Expansion: When Islam emerges in the 630s CE, the Byzantine Empire faces this challenge from a position of much greater strength. With secure control of the Mediterranean and more resources at its disposal, the empire successfully contains the initial Arab expansions. While Syria and parts of Egypt might still fall in this timeline, North Africa remains firmly Byzantine, preventing the Islamic conquest of Spain that historically occurred in 711 CE.
Territorial Continuity: By the 9th century, the Byzantine Empire still controls most of the Mediterranean coastline, including Italy, Sicily, North Africa, and parts of Spain. While some territorial losses likely occur during periods of crisis, the empire maintains its essential Mediterranean character rather than contracting to a primarily Anatolian state as it did historically.
Political Structures: The exarchate system evolves over time, with the Western territories gradually developing more distinctive administrative traditions while remaining within the imperial framework. By the 10th century, a form of "commonwealth" structure might emerge, with semi-autonomous Western provinces acknowledging Constantinople's sovereignty but managing most of their own affairs.
Alternative Feudalism: The theme system and other Byzantine administrative innovations create an alternative to Western European feudalism in the Mediterranean regions. Land ownership remains more diverse, with stronger urban centers and more limited noble power than developed in historical Western Europe.

Religious and Cultural Divergence

The religious landscape of Europe and the Mediterranean develops along dramatically different lines:

Delayed East-West Schism: With stronger political ties between Eastern and Western Christianity, the schism between the Orthodox and Catholic churches either never occurs or takes a very different form. Religious practices remain more diverse within a nominally unified church, with regional variations accommodated rather than becoming the basis for formal separation.
Different Papal Development: The Papacy evolves as an important religious office but does not develop the independent political power it historically acquired. Popes remain more integrated into the imperial church structure, with their elections requiring imperial confirmation longer than in our timeline.
Islamic Cultural Interaction: Rather than conquering large parts of the Mediterranean, Islamic civilization interacts with the Byzantine world primarily through frontier zones and trade. This creates different patterns of cultural exchange, with Byzantine preservation of Greco-Roman knowledge reducing the historical role of Islamic scholars in transmitting classical learning to Western Europe.
Preservation of Classical Culture: Greek and Roman cultural and intellectual traditions remain more continuously accessible throughout the Mediterranean. The concept of a "Dark Age" with lost classical knowledge never develops to the same extent, as urban life, literacy, and scholarly traditions maintain greater continuity.

Economic and Commercial Patterns

The Mediterranean economy develops along different lines with continued Byzantine dominance:

Unified Economic Zone: The Mediterranean remains a relatively unified economic zone longer than in our timeline, with the Byzantine gold solidus serving as an international currency well into the medieval period. Trade routes connecting the Eastern and Western Mediterranean remain more active, supporting higher levels of commercial activity.
Urban Continuity: Cities throughout the Mediterranean basin maintain larger populations and more economic significance than they historically did during the early medieval period. Rome, Carthage, Syracuse, and other Western cities avoid the dramatic population collapse they historically experienced.
Technological Diffusion: Byzantine technological innovations spread more readily throughout the Mediterranean. Techniques in agriculture, textile production, shipbuilding, and military technology diffuse more efficiently across the unified imperial space, maintaining higher overall levels of material civilization.
Different Commercial Powers: The trading cities that historically rose to prominence in the medieval Mediterranean—Venice, Genoa, Pisa, Barcelona—either develop as Byzantine provincial centers or emerge in different forms. Their commercial activities occur within the Byzantine economic sphere rather than as independent maritime republics competing with the empire.

Military and Naval Developments

Byzantine military dominance reshapes the security landscape of the Mediterranean and Europe:

Naval Technology: With continued Byzantine naval supremacy, Mediterranean shipbuilding and navigation techniques evolve differently. The Byzantine dromon (warship) remains the dominant naval vessel, with its Greek fire weapons system providing a crucial military advantage that helps maintain imperial control of the sea.
Military Organization: The theme system and other Byzantine military innovations spread throughout the empire, creating a distinctive military organization different from Western European feudal armies. Professional and semi-professional forces predominate over the knight-based systems that historically developed in Western Europe.
Fortification Patterns: Byzantine defensive architecture—characterized by scientific principles of design rather than sheer mass—becomes the standard throughout the Mediterranean. Castle development follows different patterns than the motte-and-bailey and later concentric designs that historically emerged in Western Europe.
Military Technology Transfer: Byzantine military technologies, including aspects of Eastern horse archery, body armor design, and siege engineering, diffuse more effectively throughout the Mediterranean world, creating different patterns of military development.

Intellectual and Scientific Trajectory

The preservation of Byzantine imperial structures fundamentally alters intellectual history:

Continuous Access to Classical Knowledge: Greek scientific, philosophical, and medical texts remain continuously accessible in the West, rather than being largely lost and later reintroduced through Arabic translations as occurred historically. This accelerates intellectual development in Western Europe by centuries.
Different University Tradition: Higher education develops along Byzantine lines rather than following the historical Western European university model. Centers of learning maintain closer connections to imperial administration and Orthodox religious institutions, with different curriculum emphases and organizational structures.
Scientific Advancement: With better preservation of ancient scientific knowledge and continued contact with Eastern scientific traditions, scientific progress follows a different trajectory. Fields like mathematics, astronomy, medicine, and engineering advance more continuously, without the historical medieval European focus on theological questions.
Legal Traditions: Roman law remains the foundation of legal systems throughout the Mediterranean, without the historical division between areas of Roman law influence and those dominated by Germanic legal traditions. This creates greater legal uniformity across Southern Europe and North Africa.

Global Historical Implications

The survival of a powerful, Mediterranean-spanning Byzantine Empire has profound implications for world history:

Different Crusades: The Crusades as we know them never occur, as the Byzantine Empire maintains control of the Holy Land or, if it is temporarily lost to Islamic powers, has the capability to recapture it without Western European assistance. Christian pilgrimage to Jerusalem continues under Byzantine protection.
Altered Renaissance: The Renaissance takes a different form, emerging earlier but perhaps less dramatically. Without the sharp break in classical knowledge that historically occurred, there is no need for the same kind of "rediscovery" of ancient learning that characterized the historical Renaissance.
Colonial Expansion: When the Age of Exploration eventually begins, it might be led by a still-powerful Byzantine Empire seeking new trade routes and territories. Alternatively, Atlantic-facing powers like the Franks might take the lead, but with different technological and intellectual resources than historical colonial powers possessed.
Religious Map: The religious map of Europe, North Africa, and the Middle East looks dramatically different. Islam likely remains confined to the Arabian Peninsula and parts of the Middle East, while Christianity maintains its dominance around the Mediterranean basin. Judaism might find a different place in this alternate religious landscape, potentially with more tolerance under Byzantine rule than it historically experienced in medieval Western Europe.

Expert Opinions

Dr. Sophia Paleologos, Professor of Byzantine Studies at the University of Athens, suggests:

"A successful and enduring Justinianic reconquest would have fundamentally altered the relationship between Eastern and Western Christianity. The Great Schism of 1054, which historically divided Orthodoxy and Catholicism, would likely never have occurred in the same way. Instead, we might have seen a more pluralistic Christian tradition develop, with regional variations in practice and theology accommodated within a nominally unified church. The Papacy would have evolved as an important patriarchate with special prestige due to Rome's apostolic heritage, but without the independent political power it historically developed. This would have created a very different religious landscape in Europe—perhaps more diverse and decentralized in practice while maintaining theoretical unity. The implications for everything from art and architecture to political theory would have been profound, as religious justifications for royal authority and concepts like divine right would have developed along Byzantine rather than Western European lines."

Professor Robert Harrison, historian of medieval Mediterranean economies at Oxford University, notes:

"The economic implications of sustained Byzantine control of the Mediterranean cannot be overstated. In our history, the fragmentation of the Mediterranean into competing Christian and Islamic zones created significant trade barriers and redirected commercial networks. With a unified Byzantine Mediterranean, we would have seen much higher levels of urban prosperity and commercial activity throughout the early medieval period. Cities like Carthage, Alexandria, and Rome would have maintained much larger populations and greater economic significance. The Byzantine gold solidus would have remained the dominant international currency, providing monetary stability conducive to trade. Agricultural and industrial techniques would have diffused more efficiently across this unified economic space. When we consider that much of Europe's historical economic backwardness in the early medieval period stemmed from the collapse of Mediterranean trade networks, this alternative timeline suggests a much more prosperous and economically advanced European civilization developing several centuries earlier than historically occurred."

Dr. Ahmed al-Masri, expert in comparative Islamic-Byzantine history at the American University in Cairo, observes:

"The most fascinating aspect of this scenario is how it would have altered the development and spread of Islam. Emerging in the 7th century, Islam historically expanded into territories that had either recently been Byzantine (Syria, Egypt, North Africa) or had never fully recovered from the collapse of Roman authority (Spain). A stronger, reconstituted Byzantine Empire would have presented a much more formidable barrier to Islamic expansion. This doesn't mean Islam wouldn't have become a major world religion—its appeal was not solely due to military conquest—but its geographic distribution would have been dramatically different, perhaps remaining centered in Arabia, Mesopotamia, and Persia. The intellectual and cultural synthesis that historically occurred between Islamic and Greco-Roman traditions would have taken different forms. Rather than Islamic scholars preserving and commenting on classical texts that had been lost to Western Europe, we might have seen more direct Byzantine preservation of this heritage, with Islamic intellectual contributions developing in dialogue with a still-vital Byzantine tradition rather than building upon inherited ancient knowledge in relative isolation from contemporary European thought."