What Is the Valens Aqueduct?
The Valens Aqueduct, known in Turkish as Bozdoğan Kemeri, is a Roman-period aqueduct that still spans a major traffic artery in Istanbul’s Fatih district. Construction began in the mid-fourth century and was completed during the reign of Emperor Valens in the year 373. It was built as part of a vast water-supply network created to meet the growing needs of Constantinople.
Rather than being an isolated monument, the aqueduct forms one visible segment of a huge system of channels, tunnels and bridges that brought fresh water from springs in Thrace to the imperial capital. It supplied water to public baths, palaces and large cisterns that stored water for daily life in the city.
Location and Architectural Features
The Valens Aqueduct connects two of Istanbul’s historic hills. On one side stands the hill of the Fatih Mosque, on the other the area of Istanbul University. Modern Atatürk Boulevard passes directly under the arches.
- Approximate original length: around 970 m
- Surviving length today: just over 900 m
- Average height: about 28–29 m
The structure is built from cut stone and brick in a two-storey arcade. The water channel ran along the top in a gently sloping line, allowing water to flow by gravity alone. The gradient was carefully calculated so that water moved steadily without stagnating or overflowing.
Role in the Ancient Water System
The aqueduct belonged to one of the longest ancient water systems known. Water from several spring fields in Thrace was collected and guided over tens of kilometres towards Constantinople. Large open-air cisterns and covered reservoirs, such as the Cistern of Mocius, the Cistern of Aetius, the Basilica Cistern and the Binbirdirek Cistern, stored the water and distributed it to different districts.
The Valens line was especially important for supplying the imperial quarter, the Great Palace and the areas around the Hippodrome. As the city expanded in the late Roman and early Byzantine periods, new branches and repairs kept the system functioning.
Byzantine Period
During the Byzantine era, the aqueduct underwent several phases of maintenance and partial rebuilding. Periods of siege and conflict damaged some sections, but the basic role of the system remained the same: carrying water from the countryside into the walled city.
When the city’s population shrank in the later Middle Ages, overall water demand decreased. Some branches of the system fell into disuse, while others continued to feed gardens, monasteries and small neighbourhood fountains.
Ottoman Period and Restorations
After the conquest of Istanbul in 1453, the Ottomans quickly realized the strategic value of the existing water infrastructure. The Valens Aqueduct and its connected channels were repaired to supply water to the Topkapı Palace, the Old Palace and nearby neighbourhoods.
Over the following centuries, different sultans ordered repairs and reinforcements. New waterworks, such as the Kırkçeşme system, were added to meet the needs of a growing metropolis, but the Valens line continued to function alongside these newer installations.
In the modern era, conservation and restoration projects have focused on stabilizing the masonry and protecting the aqueduct as a landmark within the historic peninsula.
The Valens Aqueduct Today
Today, the Valens Aqueduct is a striking element of Istanbul’s skyline. Although it no longer carries water, it serves as a visible reminder of how ancient engineers shaped the city’s infrastructure.
For visitors, it offers:
- An accessible example of Roman engineering in the middle of a modern city
- A visual link between the Roman, Byzantine and Ottoman layers of Istanbul’s history
- A natural stop on walking routes that include the Fatih Mosque, Istanbul University and nearby city walls
Even a short walk around the arches makes it clear how central water management was to the life and survival of historic Constantinople.