What If The Eastern Roman Empire Reconquered The West?

The Actual History

The Roman Empire's division into Eastern and Western halves became formalized in 395 CE when Emperor Theodosius I died and left the empire to his sons: Arcadius in the East and Honorius in the West. While this administrative division had precedents, it marked the beginning of increasingly divergent paths for the two regions. The Western Roman Empire, beset by economic decline, political instability, and relentless pressure from various Germanic peoples along its borders, gradually lost control of its territories.

By 476 CE, the Western Roman Empire effectively collapsed when the Germanic commander Odoacer deposed the last Western Emperor, Romulus Augustulus, and declared himself King of Italy rather than Emperor. Meanwhile, the Eastern Roman Empire—which would later be termed the "Byzantine Empire" by modern historians, though its citizens continued to identify themselves as Romans (Romaioi)—retained its strength, benefiting from its more defensible geography, wealthier provinces, and greater political stability.

In the early 6th century, Emperor Justinian I (reigned 527-565 CE) ascended to the Eastern Roman throne with ambitious plans to restore the empire to its former glory. Justinian's reconquest campaigns began in 533 CE, when his brilliant general Belisarius led an expedition that successfully recaptured North Africa from the Vandals. Emboldened by this success, Justinian turned his attention to Italy, which had been under Ostrogothic rule since Odoacer's overthrow.

The Gothic War (535-554 CE) proved to be a devastating conflict. While Belisarius initially achieved rapid success, capturing Rome in 536 and reaching Ravenna by 540, the conflict soon devolved into a protracted struggle. The Ostrogoths rallied under King Totila, who recaptured much of Italy. The war devastated the Italian peninsula, with cities depopulated, agricultural lands abandoned, and infrastructure destroyed. Eventually, the Eastern Romans prevailed under the generalship of Narses, who defeated the Ostrogoths decisively in 552 at the Battle of Taginae.

Simultaneously, Imperial forces secured footholds in southern Spain from the Visigoths in the 550s, temporarily establishing the province of Spania. However, these Western reconquests proved ephemeral. The Eastern Roman Empire had overextended itself militarily and financially. The immense costs of the campaigns, combined with outbreaks of bubonic plague (the Plague of Justinian) beginning in 541, severely weakened the empire's resources.

By the time of Justinian's death in 565, the reconquered territories were already slipping from Byzantine control. The Lombards invaded Italy in 568, conquering much of the peninsula and reducing Byzantine holdings to isolated coastal regions. In North Africa, Berber rebellions challenged imperial authority. By the early 7th century, the empire faced new existential threats from the Sassanid Persians and, later, the emergent Islamic Caliphate, forcing the abandonment of most western territories.

Justinian's ambitious reconquest ultimately failed to reunite the Roman world, instead accelerating the Eastern Empire's decline by depleting its resources at a critical juncture. The Mediterranean would remain divided, with Western Europe developing distinct political and cultural identities under Germanic successor kingdoms, later evolving into medieval feudal states, while the Eastern Empire continued as a Greek-speaking, Orthodox Christian state until its final fall to the Ottoman Turks in 1453.

The Point of Divergence

What if the Eastern Roman Empire had successfully reconquered and held the Western territories? In this alternate timeline, we explore a scenario where Justinian's ambitious reconquest program achieved lasting success, reestablishing Roman authority throughout the Mediterranean basin and fundamentally altering the course of European and Mediterranean history.

The point of divergence from our timeline could have occurred in several plausible ways:

First, the devastating Plague of Justinian, which first erupted in 541 CE and killed an estimated 25-50 million people across the Mediterranean basin, might have been less severe or geographically limited. This pandemic significantly undermined both military recruitment and tax revenues at a critical moment in Justinian's reconquest efforts. A more contained outbreak would have left the empire with greater manpower and financial resources to consolidate its gains in the West.

Alternatively, Justinian might have deployed his military resources more strategically. In our timeline, he simultaneously pursued war against the Sassanid Persians while attempting reconquests in the West, dispersing his forces and treasury. A more focused approach—perhaps concluding a lasting peace with Persia before launching western campaigns—would have allowed for more decisive victories and stronger occupation forces.

A third possibility centers on the relationship between Justinian and his brilliant general Belisarius. Historical records suggest that Justinian grew suspicious of Belisarius' popularity and potentially limited his authority and resources. In this alternate timeline, Justinian might have given Belisarius fuller support and authority, allowing him to completely destroy the Ostrogothic forces in his initial Italian campaign rather than being recalled to Constantinople in 540 CE just as victory seemed within reach.

Finally, Justinian's successors might have prioritized differently. In our timeline, Emperor Justin II (565-574) and his successors shifted focus eastward toward Persia. Instead, they might have recognized the strategic importance of the western territories and committed resources to defend Italy against the Lombard invasions of 568 CE.

In this alternate timeline, we'll explore a convergence of these factors: a less devastating plague, better strategic prioritization, fuller support for Belisarius' campaigns, and successors committed to Justinian's western vision. By 570 CE, rather than facing territorial losses, the restored Roman Empire has successfully consolidated control over Italy, North Africa, and significant portions of Spain, setting the stage for a radically different medieval world.

Immediate Aftermath

Consolidation in Italy (554-580 CE)

In our alternate timeline, the Byzantine victory over the Ostrogoths in 554 CE marks the beginning of successful reintegration rather than a hollow triumph. Unlike the actual timeline where Italy was left devastated and vulnerable to Lombard invasion, several key developments ensure Roman control:

Effective Reconstruction Program: Justinian immediately implements a comprehensive rebuilding initiative for Italian cities and infrastructure. The Pragmatic Sanction of 554 is expanded to include generous tax incentives for repopulation and agricultural restoration, preventing the extreme depopulation that occurred historically.
Military Settlement Policy: Rather than withdrawing the bulk of his forces as occurred historically, Narses oversees the establishment of military colonies (limitanei) throughout northern Italy. Veteran soldiers receive land grants in strategic areas, particularly along potential invasion routes from the Alps, creating a self-sustaining defensive network.
Integrated Administration: The Byzantine administration moves swiftly to incorporate Italian elites into the imperial governance structure. The Roman Senate, though diminished in power, is formally reestablished as a municipal council with ceremonial ties to Constantinople, giving Italian aristocrats a stake in the new order.

When the Lombards attempt their historical invasion in 568, they face not the depleted, disorganized resistance of our timeline but rather a well-defended territory with fortified passes and a population invested in maintaining Roman rule. The Lombard king Alboin is defeated and killed in battle near Aquileia in 569, and the remaining Lombard forces are either repelled or incorporated as foederati (allied troops) under Byzantine command.

Expansion in Spain (555-590 CE)

The historical province of Spania, which in our timeline remained a small coastal territory, becomes the springboard for more ambitious expansion:

Strategic Alliance with Athanagild: The Byzantine intervention in the Visigothic civil war takes a different turn. General Liberius forges a stronger alliance with the rebel Athanagild, who, upon becoming king with Byzantine support, cedes not only southern coastal regions but agrees to become a client ruler acknowledging the emperor's suzerainty.
Religious Diplomacy: Justinian's religious representatives skillfully exploit divisions between Arian Visigoths and their Catholic Hispano-Roman subjects. By positioning the empire as protector of Nicene Christianity, they foster pro-Byzantine sentiment among the Hispanic population.
Gradual Annexation: Rather than direct conquest, Byzantine influence expands through a combination of diplomatic marriages, commercial privileges, and military demonstrations. By 590, most of southern and eastern Spain has been peacefully incorporated into the empire, with Visigothic nobles integrated into the imperial hierarchy.

Administrative Innovations (565-600 CE)

Justinian's death in 565 CE brings not abandonment of his western policy but its refinement under his successors:

Creation of Western Exarchates: Building on the Exarchate system that historically developed later, Justin II establishes semi-autonomous military-civil administrations centered in Ravenna for Italy, Carthage for Africa, and New Carthage (Cartagena) for Hispania. These exarchates maintain local flexibility while ensuring loyalty to Constantinople.
Pragmatic Religious Policy: Rather than pursuing the rigid religious uniformity that historically alienated Monophysite Christians in Egypt and Syria, Justin II and his successors adopt a more tolerant approach, issuing conciliatory theological statements that ease tensions with non-Chalcedonian Christians while focusing resources on the West.
Economic Integration: The imperial government sponsors commercial networks connecting the grain-producing regions of Africa, the metallurgical centers of Spain, and the urban markets of Italy and the East. Mediterranean shipping routes are secured against piracy, maintaining the vital economic arteries of the reunified empire.

Response from the Frankish Kingdoms and Avars (570-600 CE)

The reconsolidation of Roman power changes the political calculations of the empire's neighbors:

Frankish Accommodation: The Merovingian Frankish kings, witnessing Byzantine success, shift from expansionist ambitions in Italy and Spain to a more cautious approach. Marriage alliances are established between Frankish royalty and Byzantine nobility, and formal recognition of Byzantine authority in the Mediterranean is exchanged for confirmation of Frankish control in Gaul.
Containment of the Avars: The resources freed by successful western integration allow the empire to take a stronger stance against the Avars in the Balkans. Rather than the historical pattern of tribute payments, Byzantine forces establish a more effective defensive line along the Danube, supplemented by diplomatic arrangements with Slavic tribes willing to act as buffers against Avar expansion.

By the beginning of the 7th century, the immediate aftermath of successful reconquest is a Mediterranean world once again dominated by Roman imperial structures. While not identical to the unified empire of Augustus or Trajan, this restored Roman state has successfully adapted ancient institutions to post-migration realities, creating a hybrid political system that balances central authority with regional autonomy, military security with economic revival, and Roman traditions with new administrative necessities.

Long-term Impact

Resilience Against Islamic Expansion (634-750 CE)

The emergence of Islam and the rapid Arab expansion that historically transformed the Mediterranean world encounters a fundamentally different geopolitical landscape in this alternate timeline:

Unified Mediterranean Defense: Rather than facing a fragmented response from Byzantine territories in the East and various successor kingdoms in the West, the expanding Caliphate confronts a unified imperial defense system spanning from Anatolia to Gibraltar. Naval resources from Egypt, Africa, and Sicily are coordinated to maintain Mediterranean dominance rather than operating independently.
Containment Rather Than Conquest: While the initial Arab conquests of Syria and Egypt likely still occur due to local religious tensions and the exhaustion from the Byzantine-Sassanid wars, the unified empire prevents further expansion. North Africa remains firmly under Roman control, and the crucial naval battle at Phoenix (historically called the Battle of the Masts, 655 CE) results in a Byzantine victory rather than defeat.
Absence of Iberian Conquest: Without the Visigothic collapse that historically allowed Muslim forces to cross into Spain in 711 CE, Iberia remains part of the Roman world. This dramatically alters the balance of power, as the resources that historically supported both Umayyad Spain and resistance to it instead reinforce Roman Mediterranean hegemony.
Cultural Exchange Rather Than Conquest: Islamic influence still enters the Mediterranean world, but through trade and intellectual exchange rather than political domination. Byzantine scholars preserve and translate early Arabic scientific and philosophical works, while Roman engineering and administrative practices influence Caliphate development.

Religious Evolution and the Great Compromise (700-900 CE)

The religious landscape evolves differently without the deep East-West divide that historically culminated in the Great Schism:

Pragmatic Ecclesiastical Federalism: The necessity of accommodating diverse Christian traditions across the reunified empire leads to a more decentralized church structure. Regional patriarchates (Rome, Constantinople, Alexandria, Antioch, Jerusalem, and eventually Carthage and Toledo) develop distinctive liturgical practices while maintaining communion.
The Synod of Syracuse (763 CE): This pivotal church council, with representatives from all major Christian centers, establishes the "Doctrine of Distinct Expressions," which formally acknowledges that different theological formulations and practices may express the same essential faith. This prevents the hardening of positions that historically led to schism.
Iconoclasm Moderated: The iconoclastic controversy that historically divided Byzantium is resolved more quickly and less traumatically. Western influence, particularly from Rome and the monastic traditions of Italy, tempers the more extreme iconoclastic positions, resulting in regulated rather than prohibited religious imagery.
Missionary Coordination: The evangelization of Slavic peoples proceeds as a coordinated imperial policy rather than competitive efforts between Eastern and Western churches. Methods similar to those historically employed by Saints Cyril and Methodius are applied more broadly, creating a more gradual Christianization that respects local cultures.

Political Evolution and Administrative Adaptation (750-1100 CE)

The reconstituted empire undergoes significant internal transformation to maintain cohesion across its vast territories:

The Thematic Revolution Expanded: The thematic system (combining civil and military authority in provincial units) develops throughout the empire, not just in its eastern territories. Italian, African, and Hispanic themes create a network of regional military-administrative units that provide both defensive strength and political integration.
Imperial College System: To maintain unity across culturally diverse regions, an expanded imperial education system develops. Provincial colleges in major cities from Syracuse to Cordoba train local elites in Roman law, administration, and military science, creating a trans-Mediterranean governing class with shared values and methods.
The Charter of Constantinople (842 CE): This constitutional reform, issued during a period of imperial strength, formalizes the relationship between central imperial authority and regional powers. It establishes an Imperial Senate with representatives from all regions and codifies the rights and responsibilities of provincial elites within the imperial framework.
Technological Preservation and Diffusion: The preservation of a unified Mediterranean economic zone prevents the technological regression that historically affected Western Europe. Roman engineering techniques, agricultural methods, and urban infrastructure are maintained and evolved throughout the empire's territories.

Economic Patterns and Commercial Development (800-1200 CE)

The economic structure of medieval Europe takes a dramatically different form:

Mediterranean Commercial Continuity: Unlike the historical shift toward northern European economic centrality, the Mediterranean remains the primary commercial artery of European civilization. Alexandria, Carthage, Naples, and Ravenna flourish as major commercial hubs alongside Constantinople.
Monetary Stability: The Roman gold solidus/nomisma remains the dominant international currency across Europe and the Mediterranean, preventing the monetary fragmentation that historically occurred. This stability facilitates long-distance trade and more sophisticated financial instruments.
Agricultural Revolution: The so-called "medieval agricultural revolution" occurs centuries earlier and more uniformly across former western territories. Irrigation techniques from Byzantine Egypt and Syria are systematically applied to Italy and Spain, dramatically increasing agricultural productivity.
Industrial Continuity: Roman industrial techniques in metallurgy, ceramics, and textile production evolve without the disruptions that historically occurred. By 1000 CE, manufacturing centers in Italy, Greece, and Spain are producing goods of quality and scale that historically wouldn't be achieved until the late medieval period.

Cultural and Intellectual Developments (900-1300 CE)

The preservation of a unified Roman world fundamentally alters intellectual history:

No "Dark Ages" in the West: The cultural and intellectual regression that historically affected Western Europe is largely avoided. Libraries, educational institutions, and intellectual traditions maintain continuity, with classical knowledge preserved and expanded throughout the Mediterranean basin.
Classical-Medieval Synthesis: Rather than the sharp break between classical and medieval worldviews that historically occurred, a more gradual evolution of thought develops. Aristotelian natural philosophy, Neoplatonic metaphysics, and Christian theology coexist and cross-fertilize throughout the empire's intellectual centers.
Technological Innovation: The preservation of ancient engineering knowledge, combined with new developments, accelerates technological progress. Water-powered industrial machinery, principles of optics, and mechanical devices develop earlier and diffuse more widely than in our timeline.
Preserved Ancient Works: Many classical texts lost to Western Europe in our timeline remain in continuous circulation. Complete versions of works by Aristotle, Tacitus, Greek dramatists, and others never experience the historical period of loss and rediscovery.

Relationship with Northern Europe (1000-1400 CE)

The empire's interaction with regions beyond its borders creates different patterns of development:

Cultural Diffusion Rather Than Conquest: Instead of the Norman conquests that historically brought southern Italy and Sicily under northern European influence, cultural and commercial exchange flows predominantly from south to north. Germanic and Frankish kingdoms adopt Roman administrative techniques, architectural styles, and educational methods.
The Northern Renaissance: The cultural and intellectual flowering that historically occurred in Italy during the 14th-16th centuries instead develops as a process of northern Europeans consciously adopting and adapting the continuous Roman-Byzantine traditions. Paris, London, and Cologne become centers of this "Northern Renaissance" by the 12th-13th centuries.
Religious Harmony and Reform Movements: Without the East-West schism, religious reform movements that historically led to Protestantism instead occur within a unified church framework. Monastic reform, challenges to clerical privileges, and calls for doctrinal clarification emerge as regional movements within a flexible ecclesiastical structure.

By the early modern period (c. 1400-1500 CE), this alternate world features a Mediterranean still dominated by a Roman Empire that, while transformed in many ways from its ancient form, maintains institutional, cultural, and economic continuity with the classical past. The historical divides between Eastern and Western Christianity, between Byzantine and Latin cultural spheres, and between Islamic and Christian Mediterranean powers have been replaced by a more integrated, though still diverse, civilizational framework centered on a Roman identity that has successfully adapted to changing conditions while preserving its essential character.

Expert Opinions

Dr. Alexios Stavridis, Professor of Byzantine Studies at the University of Athens, offers this perspective: "The failure of Justinian's reconquest represents one of history's great 'might-have-beens.' Had the empire successfully reintegrated the western territories, we would likely see a dramatically different religious landscape today. The theological divisions that eventually produced the Great Schism between Eastern and Western Christianity might have been resolved through ongoing dialogue and compromise. More importantly, the institutional strength of a unified Mediterranean empire would have created very different conditions for religious development—likely moderating the dogmatic hardening that occurred when Eastern and Western Christianity evolved in isolation from each other. The Islamic conquests, too, would have encountered a more formidable and unified response, potentially containing their expansion to the Arabian Peninsula and parts of the Near East."

Professor Eleanor Montgomery, Chair of Medieval European History at Oxford University, presents a contrasting economic analysis: "A successfully reconquered and integrated western Mediterranean under Byzantine control would have preserved the ancient economic unity of the region, with profound consequences for development patterns. The 'feudal' economic system that characterized medieval Western Europe arose largely because of the collapse of long-distance trade networks and urban markets following the Western Empire's disintegration. With these networks preserved under Byzantine administration, we would likely have seen much earlier development of sophisticated commercial institutions, banking systems, and industrial production. However, this might have come at the cost of the distinctive economic innovations that emerged from northern European feudalism—particularly the property rights regimes and competitive state systems that some historians credit with enabling the eventual rise of capitalism."

Dr. Hassan Al-Jabouri, Specialist in Comparative Mediterranean Civilizations at the American University of Beirut, adds: "The cultural implications of a sustained Byzantine reconquest would be profound beyond religion and economics. The intellectual heritage of classical antiquity would have experienced continuous development rather than the disruption and later 'rediscovery' that characterized our timeline. Arabic intellectual contributions would still have occurred but would have been integrated into an existing Greco-Roman framework rather than serving as the primary preservers and transmitters of classical knowledge. Perhaps most significantly, the sharp civilizational divides that historically emerged between 'European,' 'Byzantine,' and 'Islamic' worlds would be replaced by more gradual cultural gradients across a Mediterranean space maintaining some degree of political and economic integration. The conceptual opposition between 'East' and 'West' that has so profoundly shaped modern geopolitics might never have developed in such a timeline."