The Harbour of Kaisarius was one of the smaller but historically important harbours along the southern shore of Constantinople. Its origin, name, and role in the city’s defense and naval operations reveal both Byzantine administrative practices and military strategy City Tours Istanbul.
Possible Origins of the Name
The exact person after whom the harbour was named remains uncertain. The historian Du Cange suggests three possible candidates:
Kaisarius, Prefect of the City under Emperor Valentinian.
Kaisarius, Praetorian Prefect under Theodosius I.
Kaisarius, an important figure during the reign of Leo I.
Of these three, the last option appears most likely. The Notitia, a record of the city’s administrative districts during the reign of Theodosius II, does not mention the harbour, suggesting that it did not exist in the early fifth century. Therefore, it is probable that the Harbour of Kaisarius was constructed toward the end of the fifth century, making it a relatively late addition to Constantinople’s network of southern ports.
Location on the Sea of Marmara
The harbour’s location on the Sea of Marmara is clear from historical sources. It is often mentioned alongside the Harbours of Julian and Hormisdas. During the reign of Phocas, the tyrant emperor, troops were stationed at these harbours to prevent the landing of Heraclius on the southern side of the city.
Later, in 673, Emperor Constantine IV (Pogonatus) stationed ships in the Harbour of Kaisarius armed with Greek fire, the newly invented incendiary weapon. These ships awaited the Saracen fleet approaching from the Aegean, demonstrating the harbour’s strategic importance in defending Constantinople from naval attacks The Neorion at the Heptascalon.
The Neorion at the Heptascalon
The Neorion at the Heptascalon is another harbour mentioned in this area. Byzantine writers use the term “Heptascalon” in two main contexts. First, in its corrupted form, it marks the site of a church dedicated to St. Acacius. The earliest reference to this church appears in the writings of Constantine Porphyrogenitus, in his biography of Basil I, who restored the building.
Second, the historian Cantacuzene uses the term to indicate the location of the harbour itself, showing that the Neorion at Heptascalon was recognized as a maritime installation as well as a landmark associated with religious architecture. This dual use of the term reflects how Byzantine writers combined topographical, religious, and administrative information when describing parts of the city.
The Harbour of Kaisarius, likely named after a prominent official from the reign of Leo I, and the Neorion at the Heptascalon were key components of Constantinople’s southern port system. Positioned on the Sea of Marmara, they served both commercial and defensive purposes, providing mooring for ships, stations for military forces, and even points from which Greek fire could be deployed against invaders. Their historical references, though sometimes sparse or uncertain, highlight the strategic planning behind the city’s harbour network and the way harbours were intertwined with imperial administration, defense, and religion.
