Why Did Constantine Choose Byzantium (Later Constantinople and Istanbul) as His New Capital?

In 330 AD, Roman emperor Constantine the Great made a monumental decision that would shape the course of history: he chose the ancient city of Byzantium as the new capital of the Roman Empire, later renaming it Constantinople. This choice was not random but a calculated move driven by a combination of strategic, economic, and political factors. Situated at the crossroads of Europe and Asia, with access to key trade routes and natural defenses, Byzantium offered the perfect location for the emperor’s vision of a renewed and unified empire. Constantine’s decision would lay the foundation for what would later become the Byzantine Empire, a powerful force in world history for over a millennium.

Byzantium

Byzantium was already an ancient Greek settlement, founded around 667 BC by Greek colonists from Megara. Its location on the Bosphorus Strait made it a key site for controlling trade routes between Europe and Asia, as well as access to the Black Sea. Its founder, Byzas, chose the site due to its natural harbor and defensive advantages, ensuring Byzantium’s early prosperity as a trading hub.

Sunset behind the historic peninsula of Istanbul, where Byzantium was founded
Sunset behind Istanbul’s historic peninsula, where Byzantium was founded. A photo I took aboard a ferry in 2015. From left to right, the silhouettes of the Blue Mosque, Hagia Sophia, Beyazıt Tower, New Mosque, and Süleymaniye Mosque can be seen.

A fun fact: the first settlement founded in modern-day Istanbul was not Byzantium, but Chalcedon. Chalcedon, established around 685 BC on the eastern shore of the Bosphorus (modern-day Kadıköy), predates Byzantium by about 18 years.

Chalcedon was known as the “city of the blind” due to a remark by the Greek historian Herodotus. This phrase came about because of the city’s unfortunate geographic choice compared to the nearby location of Byzantium (modern-day Istanbul).

The story goes that when the founders of Chalcedon established their settlement in 685 BC, they overlooked the far more strategic and advantageous site directly across the Bosphorus, where Byzantium would later be founded. The Byzantium site, chosen by settlers about 17 years after Chalcedon, offered superior natural defenses and control over the vital sea passage between the Black Sea and the Aegean.

Herodotus and other ancient commentators suggested that the founders of Chalcedon must have been “blind” not to recognize the superiority of the site that Byzantium eventually occupied. Hence, the label “city of the blind” became attached to Chalcedon, emphasizing the strategic misstep of its founders in not choosing the more advantageous location.

Okay, back to Byzantium. In the 5th century BC, Byzantium fell under Persian control during the Greco-Persian Wars but later became a part of the Delian League, an Athenian-led alliance. The city thrived under Greek influence but remained relatively small compared to larger Hellenistic cities.

During the Roman era, Byzantium came under Roman rule and became significant for its strategic position. In 196 AD, Emperor Septimius Severus besieged and destroyed the city after it supported his rival in a Roman civil war. However, he later recognized its importance and rebuilt it.

In 330 AD, Constantine the Great recognized Byzantium’s immense strategic value and transformed it into the new capital of the Roman Empire, renaming it Constantinople. This marked the beginning of Byzantium’s rise as a central hub for the Byzantine Empire, which would last for over a millennium.

Head of the Colossus of Constantine, Capitoline Museums, Rome.
Head of the Colossus of Constantine, Capitoline Museums, Rome. Photo by Merulana – Own work, CC BY-SA 4.0, Link

Why Did Constantine the Great Choose Byzantium as His New Capital?

Constantine recognized the shifting power dynamics of the Roman Empire from the declining and depopulated West to the wealthier cities of the East. His choice of Byzantium as the new capital was influenced by its strategic importance in defending the Danube from barbarian invasions and protecting Asia from the Persian threat. The city’s location also allowed him to control key shipping routes between the Black Sea and the Mediterranean. The defeat of Licinius (c. 265 – 325, Roman emperor from 308 to 324), Constantine’s rival, marked the victory of a Christian and Latin-speaking Rome over a Greek-speaking, pagan-influenced Eastern power.

The decision to establish a new Eastern capital symbolized the integration of the East into the Roman Empire as a unified whole, representing learning, prosperity, and cultural preservation. Several cities were considered, including Serdica (modern-day Sofia), Sirmium, and Thessalonica. Constantine reportedly remarked, “Serdica is my Rome.” However, Byzantium’s already existing Roman infrastructure, rebuilt under Septimius Severus (a Roman politician who served as emperor from 193 to 211) and Caracalla (188 – 217), Roman emperor from 198 to 217 AD), and its strategic location ultimately made it the ideal choice for Constantine’s new capital.

Several strategic, political, and economic factors influenced this decision:

1. Strategic Location

Byzantium was located on the Bosporus Strait, which connects the Black Sea to the Mediterranean. This strategic position allowed control over important trade routes and military passage between Europe and Asia. It was ideal for defending the empire from invasions, particularly from the eastern frontiers, which were vulnerable to attacks from Persia and later, other groups like the Goths and Huns.

Side note – even about 1500 years later, Napoleon himself would recognize the strategic importance of Istanbul.

2. Already Existing Roman Infrastructure

As explained above, earlier emperors recognized the strategic importance of the city and had significantly modernized its urban structure, including fortifications, roads, and public buildings, ensuring Byzantium was well-prepared to become the center of Constantine’s vision for a revitalized Roman Empire.

3. A Huge Natural Harbor

The Golden Horn (Turkish: Haliç) is a natural harbor in Istanbul, forming a deep, sheltered inlet off the Bosphorus Strait. Its name comes from its horn-shaped, curved appearance and the golden hue that reflects during sunsets.

For Byzantium, the Golden Horn was crucial due to its geographical advantages. A long sliver of a river estuary, the Golden Horn is sheltered from the swift currents of the Bosphorus. This made it a naturally protected port, allowing the city to dock and control commercial and military ships securely. It is also big enough to hold hundreds, even thousands of ships.

Surrounded by water on three sides, the inlet also added a defensive barrier against potential naval attacks, making the city harder to siege. Byzantium thrived as a trading hub, with the Golden Horn connecting trade routes between Europe and Asia. Its sheltered waters and accessibility made it an ideal harbor for maritime commerce and defense.

Byzantium map: Golden Horn
The Golden Horn, a long river estuary sheltered from the swift Bosphorus currents, served as a natural harbor for Byzantium. Its calm waters allowed for the safe docking of commercial and military ships, making it an essential part of the city’s defense and trade. Capable of holding thousands of vessels, it also provided a protective barrier against naval attacks, solidifying Byzantium’s position as a thriving trading hub connecting Europe and Asia. The first bridge on the Golden Horn, built by Byzantine Emperor Justinian the Great, is shown near the Theodosian Walls (see upper right) in this rendering of old Constantinople. Northwest is up. Image source: Wikipedia

4. Economic Benefits

The location of Byzantium made it a bustling hub for commerce, strategically positioned at the crossroads of major trade routes connecting the East and West, including the famous Silk Road. This prime location allowed the city to dominate the passage of goods between Europe and Asia. Byzantium’s access to both the Mediterranean Sea and the Black Sea made it a vital center for maritime trade, where goods like silk, spices, precious metals, and textiles passed through its harbors.

Orthographic projection of the main routes of the Silk Road
Orthographic projection of the main routes of the Silk Road. It was a network of Eurasian trade routes active from the second century BCE until the mid-15th century. Spanning over 6,400 km (4,000 mi), it played a central role in facilitating economic, cultural, political, and religious interactions between the Eastern and Western worlds. Note that the western end of the route terminated in Constantinople (formerly Byzantium, now Istanbul). Image: Wikipedia CC BY-SA 4.0

By controlling Byzantium, the Roman Empire not only secured its military presence in the region but also gained significant economic benefits. The empire could impose taxes on the vast quantities of goods flowing through the city, greatly boosting its treasury. Byzantium’s role as a trade hub also fostered cultural exchange, turning it into a melting pot of ideas, goods, and people from different parts of the world.

The Greek historian and geographer Strabo (64 or 63 BC – c. 24 AD) wrote about the Bosphorus and its abundant fish, particularly noting the region’s richness in fish species. He also mentioned that the fish could be easily caught due to their large numbers, the strength of the current, and the narrowness of the inlets. In fact, the fish were sometimes even caught by hand (it was still like that as late as the 1960s).

The abundance of fish made the Bosphorus a significant fishing area in ancient times, benefiting both Byzantium and other nearby settlements.

Even as late as the 1960s, it was possible to easily catch large quantities of fish in the Bosphorus using just a simple scoop.
Even as late as the 1960s, it was possible to easily catch large quantities of fish in the Bosphorus using just a simple scoop.

5. Defensible Geography

Byzantium had a natural advantage due to its geographic features. It was surrounded by water on three sides (the Sea of Marmara, the Bosporus, and the Golden Horn), making it easier to defend against naval and land-based attacks. The landward side of the city was protected by natural barriers and, later, fortified by strong walls (the famous Theodosian Walls).

Plus, the strong currents that flowed through the narrow channel (the Bosphorus) would make it very difficult for any army to attack by the sea.

Any attackers who wanted to take the city were able to approach from only one direction (north), and this side was later protected by the Theodosian walls.

Constantinople historic rendering
A rendering of Constantinople shows the Golden Horn on the left, the Bosphorus on the upper left, and the Sea of Marmara on the upper right. Hagia Sophia is visible at the southern end of the peninsula, near the Sea of Marmara. The current structure was built by Byzantine Emperor Justinian I between 532 and 537 as the Christian cathedral of Constantinople. The Theodosian Walls can be seen at the bottom of the image. These double walls, constructed during the reign of Emperor Theodosius II (r. 402–450), are located about 2 km west of the original Constantinian Wall. The first phase, overseen by Anthemius, was completed in 413. Earthquakes in 437 and 447 caused significant damage, but Theodosius II ordered the repairs, restoring the walls in just 60 days. A second outer wall and moat were likely added at this time for additional defense. This image shows the restored version of the Theodosian Walls.

6. Military Considerations

Byzantium’s location was more central to the eastern provinces, where much of the Roman Empire’s military focus lay during Constantine’s reign. The eastern provinces were wealthier and more populated than the western provinces, making it essential to have a capital close to the empire’s economic and military core. Additionally, the proximity to the Danube frontier allowed for rapid military responses to threats in the Balkans.

7. Desire for Political Stability and a Fresh Start

By the early 4th century, Rome’s position as the capital had become increasingly untenable due to its distance from the more prosperous eastern provinces and growing political instability. The Roman Senate and various factions continually vied for influence, creating a complex and difficult governance situation.

Constantine recognized that establishing a new capital in Byzantium offered a strategic advantage. Located near the wealthier and more stable eastern provinces, it was well-positioned for both military and economic purposes. By moving the capital, Constantine distanced himself from the entrenched power struggles and declining influence of old Rome, allowing him to create a fresh center of authority free from the dominance of the traditional aristocracy.

This new capital, Constantinople, symbolized the start of a new era for the Roman Empire-one that reflected Constantine’s vision of a unified, Christian empire. In renaming the city after himself, he underscored his intent to shift the empire’s focus from its troubled past to a prosperous and stable future, with Constantinople at the heart of a revived and reimagined Roman state.


In summary, Byzantium offered Constantine a unique blend of strategic, military, and economic advantages, combined with the opportunity to create a new imperial and Christian center. This decision laid the foundation for the Byzantine Empire, which would last for over a thousand years until the fall of Constantinople in 1453.

Sources

Özgür Nevres

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