Historical and Archaeological Context
Constantinople and the longest Roman aqueduct

The Flourishing City
The Roman city of Byzantium on the natural boundary between Europe and Asia, was re-founded as Constantinopolis in AD 330 by the emperor Constantine. Taking on the mantle of old Rome, the city became a focus for imperial patronage and display, quickly acquiring the grand urban structures expected of any classical metropolis; the fora, baths, colonnaded streets and hippodrome. The walls of the old city were expanded and within two decades the urban population began to grow exponentially. At a time when many western cities stagnated or shrunk in size, late antique Constantinople expanded and flourished in both cultural and physical wealth, to provide a secure urban setting for the eastern empire into the later middle ages. Medieval Byzantium was renowned and admired as a centre of Christian art and culture until the 15th century when the city finally fell to the Ottoman conqueror Mehmet II.

Fragmentary relics survive from the Byzantine city, but much has been lost or lies buried beneath the later Ottoman city and Turkish Istanbul. Yet the fundamental necessities for urban existence in the early medieval world, religion, security and sustenance, are represented in three of the city's greatest surviving monuments. The sixth-century emperor Justinian's finest achievement, the church of Hagia Sophia, dominates the Istanbul skyline and the western extent of the old city is still marked by Theodosius' fortification scheme of AD 415. The third structure is the Bozdogan Kemeri, a great water bridge of some 86 arches spanning one of the city's busiest highways and normally identified as the Aqueduct of Valens (Dalman 1933; Mango 1995). According to a contemporary source this emperor welcomed the Thracian nymphs and waters to the thirsty city, transported there by the new 'overground and underground river' (Greg. Naz. PG. 36.221C).

The Long-Distance Aqueduct
Given the monumentality of the Aqueduct of Valens, it is sometimes hard to imagine that it was originally conceived as only a single component of a much grander scheme, which had probably been started in around AD 345. This was a vast and complex system, which supplied the city with water from a variety of sources in Thrace. At over 250km, it is the longest water supply line known from the ancient world and it remains one of the greatest achievements of hydraulic engineering. More than 30 stone water bridges and many kilometers of underground tunnels carried the water over mountain and plain from the plentiful springs of the Istranja mountains near Vize straight into the heart of the city.

Such was the magnificence of the undertaking that it even appears to have received its own popular mythology in the city it watered: an Ottoman writer was later to claim that the aqueduct had drained the great Danube river itself (Evliya Çelebi, Seyahatname, I, 484). The known system is at least two and half times the length of the longest recorded Roman aqueducts at Carthage and Cologne, but perhaps more significantly it represents one of the most outstanding surveying achievements of any pre-industrial society.

The Later History of the Water Supply
The historical sources record the continuing maintenance of the system until the early 7th century. However in AD 487 the aqueduct was reportedly cut by the Goth Theodoric Strabo and it was also apparently damaged during the Avars seige of the city in 626. Restoration of the long-distance system is not recorded until AD 767 in the reign of Constantine V. Some historians have interpreted this 150 year hiatus marking the end of the 'classical water system', with dire consequences for the maintenance of a large urban population (Mango 1995). Magdalino (1996) adopts less pessimistic position and has recently questioned this interpretation of the city's demographic decline. Neither account however considers the possibility that the sources closer to the city were continuously (or even increasingly) exploited during this period (See sections on Halkali and the Forest of Belgrade).

Throughout the middle ages the water bridges and channels were disrupted by earthquakes, so that by the late 12th century the long-distance system is said to have been abandoned as a result of cumulative seismic damage. Like the Anastasian Wall, the final reference to the aqueducts was in a nostalgic late 15th century list of the Wonders of Constantinople. After the fall of the city to the Ottomans, a new system was constructed in the 16th century based entirely on the closer sources at Halkali and in the Forest of Belgrade.