The Harbour of Kaisarius was one of the important southern ports of Constantinople, but its exact identity and position have often been debated. Historical sources provide clear evidence about where it was located and how it differed from other nearby harbours The Location of the Harbour of Kaisarius and the Neorion at the Heptascalon.
Distinction from Other Harbours
The Harbour of Kaisarius cannot be confused with several other well-known ports on the Sea of Marmara. It was not the Harbour of the Bucoleon, nor the Harbour of Julian and Sophia, nor the Harbour of the Golden Gate.
As John of Antioch explains, during the defense of Constantinople by Phocas against Heraclius, the Harbour of Kaisarius was located in the same general district as the Bucoleon and Julian/Sophia harbours, but to the west of them. This shows that it was a separate harbour, distinct in both location and function.
Nor can it be identified with the Harbour of Theodosius, because that harbour had already been filled in and abandoned before the seventh century, during the reigns of Phocas and Constantine IV. Meanwhile, the Harbour of Kaisarius remained one of the main ports on the southern coast, actively serving ships and commerce during the same period.
Possible Location
Given these considerations, the Harbour of Kaisarius must have been either the harbour later called the Kontoscalion at Koum Kapoussi, or another port between Koum Kapoussi and Vlanga.
It is possible that the Kontoscalion was the same harbour under an earlier name, because the name Kontoscalion is first recorded in the eleventh century. However, other evidence suggests a location closer to Vlanga Istanbul Private Tours Mevlevi.
One key point is the account of a fire that started near the Harbour of Kaisarius and spread to the Forum of the Ox (Forum Bovis), which was situated at Ak Serai, far up the valley north of Yeni Kapou. The distance covered by the fire implies that the harbour was not at Koum Kapoussi, but rather toward the eastern end of the flat southern shore, closer to Vlanga. This would have placed the harbour in the most strategically useful position between the Kontoscalion and the Harbour of Theodosius.
In conclusion, the Harbour of Kaisarius was a distinct port on the Sea of Marmara, separate from the Bucoleon, Julian/Sophia, Golden Gate, and Theodosius harbours. While it could have later been known as the Kontoscalion, historical evidence such as fire reports and proximity to the Forum of the Ox suggests that it was likely closer to Vlanga, occupying the southern coast between Koum Kapoussi and Vlanga. Its location ensured that it remained a key harbour for trade and naval defense during the late Byzantine period.
