Camped before the walls of Constantinople, the army of the First Crusade must have been in need of a bath after slogging across the Balkans in 1097. Within the great circuit, the most powerful fortifications in Europe, was a city replete with richly decorated churches and fine monuments serving a population of possibly around a quarter of a million people, greater than any other in Europe at the time. But what most impressed William of Malmesbury, an Anglo-Norman chronicler of the Crusade, was the city’s urban water supply. This was managed through sluices and drains that cleaned the streets before emptying into the surrounding sea. Although he was writing some 30 years after the arrival of the crusaders, his account retains the contemporary legend known from Arab and other accounts that the waters were sourced at the distant Danube, delivered through hidden channels, and then dispersed through drains into the sea. Running water and urban sewers were unknown utilities in medieval towns like Paris or London, but Byzantine Constantinople retained the legacy of its 4th-century foundation and an infrastructure established by Constantine and his successors.
The ‘wonderful works’
Today Istanbul, astride the Bosporus waterway in both Europe and Asia, is the largest city in Europe with a population in excess of 17 million. For 1,700 years, it was an imperial city, first for the East Romans or Byzantines and, after 1453, the Ottomans. For much of late antiquity and the Middle Ages, it was among the largest cities around the Mediterranean, requiring food and water resources from great distances. Unlike Rome, which has a river, springs, and other water sources in nearby hills, Constantinople was surrounded by sea on three sides, with only a minor perennial stream and one aqueduct constructed in the time of Hadrian (reigned 117-138) to supply its predecessor, Byzantium. The new expanding city required water for the growing population and it needed a new gravity fed system to provide the water to the higher elevation of the new urban area. Two major construction campaigns in the 4th and 5th centuries resulted in the building of the most extensive water supply system in the ancient world, reaching not quite as far as the Danube, but sinuously covering 267km through the forested hills to the west of Constantine’s new city.
The main visible relic of this system in the modern city is the Bozdoğan Kemer or Aqueduct of Valens, which straddles a major city highway like a giant comb separating out the traffic lanes. The bridge is 971m long, running between the city’s third and fourth hills, and originally allowed the legendary ‘Danube’ waters to reach the ceremonial heart of the city around the Great Palace, Hippodrome, and Church of Hagia Sophia. The bridge was restored a number of times by the Ottoman Sultans, and was still functioning as a water bridge into the 20th century, but remains essentially a 4th-century structure. The Aqueduct of Valens is a visible reminder of imperial munificence, both Byzantine and Ottoman, but beneath the streets of the old city are the surviving traces of more than 200 cisterns, a hidden memory of the fabric of the Byzantine city of which little survives above pavement level. The study of the ancient water features in the city goes back to the 16th century, when the first accounts appear of those Byzantine remains surviving among the new buildings of Ottoman Istanbul. However, the first serious documentation of the cisterns was published in 1893 by an Austrian Classical archaeologist and a German civil engineer. This seminal study was supplemented by further observations throughout the 20th century. The earlier Roman aqueduct of Hadrian was sourced in the Forest of Belgrade to the north-west of the city, and this fed the restored Ottoman systems until the late 19th century. Here the great 16th-century bridges built and restored by the Ottoman architect Sinan still survive, but many retain traces in their foundations of Roman and Byzantine works.
Until the final two decades of the 20th century, much less was known of the long-distance system stretching to the region known as Eastern Thrace (Trakya). A long wall from the Black Sea to the Sea of Marmora was built in the 6th century by the emperor Anastasius, 65km west of Constantinople and 56km in length, intended to provide an outer bulwark to defend the city against barbarian threats from across the Danube and the Balkans. It is a reminder that the main military danger for Constantinople and, later, for Istanbul came from the west. In more recent times – until 1990 – the region of the Long Walls and the aqueducts was a military zone, with very limited access for archaeologists or tourists. This changed with the fall of Communism, and in 1994 I was able to gain a permit from the Turkish Ministry of Culture to begin documenting the remains of the Anastasian Wall. Once we began recording the Wall structures, we became aware of the extensive remains of the aqueducts and channels preserved within the dense Thracian woodland. At the same time, the doyen of Ottoman hydraulic engineering, Prof. Kâzım Çeçen of Istanbul Technical University, turned his attention – after a career documenting Ottoman hydraulic achievements – to the Thracian aqueduct system, and the resulting study was published in 1996, in a well-illustrated volume titled The Longest Roman Water Supply Line. With the help of helicopter reconnaissance, he was able to provide for the first time a map showing the full extent of the channels and aqueducts extending past the modern town of Vize.
Very few inscriptions survive on the aqueduct bridges. One, now lost, was recorded from close to the bridge at Ballıgerme, a high single-span bridge set over a rocky gorge. The inscription dates from the early 11th century and records reconstruction of ‘the wonderful works’ after damage by nature and the enemy. Although the structure is unspecified, none other survives in the neighbourhood, and masonry from that period can be recognised in the bridge structure. Investigating the lines of the channels and bridges where they are best preserved in the forests, often with the help of local villagers, is typically slow but rewarding. During our fieldwork, conducted less than 70km from the largest city in Europe, we often felt a thrill comparable to that experienced by the discoverers of Mesoamerican monuments, as great stone bridges emerged from the Thracian forest.
Our project evolved over time. First, we were concerned to map in more detail the outline defined by Prof. Çeçen, and then to describe and document the structures and channels within a historical context, resulting in a monograph published in 2008. Another project followed, in which we worked with Istanbul Technical University to investigate the application of satellite imagery and remote-sensing. As the GPS technology improved and became more accessible, we were able to carry out higher-resolution GPS recording, which proved an important resource for our next stage. Between 2014 and 2017, we began a new project with civil engineering colleagues at the University of Edinburgh – ‘Engineering the Water Supply of Byzantine Constantinople’ – with funding for two PhD engineering students to study the channels and topography outside the city, and the distribution and storage of water within it. This was a truly interdisciplinary study that presents a rigorous basis to inform both the historical and archaeological accounts of the city.
‘The city thirsts’
As the new city grew in population and space, Themistius – the court orator in the 360s – recognised the problem of the demand for water when he wrote that ‘the city thirsts’. This remark had nothing to do with sudden drought or long-term climate change; it was quite simply a response to the fact that the city could not satisfy the demands of its growing population and the extension of the urban area on to higher ground. A new aqueduct was needed, which was built at huge cost and required exceptional expertise in planning and construction. The water was sourced from distant springs in Thrace and construction can be dated to two main phases, initiated by Constantius II from c.340 and completed in 373 under Valens. There were two lines, one rising at springs near Danamandıra, and a second at Pınarca. They joined near the village of Akalan, with a total estimated length of 246km.
The channels were cut into the sides of the hills, and lined with mortared stone and waterproof mortar covered with a stone vault. Most were c.1m wide, with some up to 1.6m high. The water was gravity-led, and there was a shallow gradient as the channels sinuously followed the contours of the Thracian hills. Bridges were constructed where the valleys were too deep, to reduce overall channel length. From this first phase, 36 bridges are known, with two long tunnels, one at Akalan to allow the two branches to join. Although no physical traces survive, the topography demands a tunnel 2km in length. A second tunnel was required further downstream at Tayakadın, where construction of the south-west corner of the new Istanbul airport has obscured part of the line. From there, the channels continue along the Alibey valley, a tributary of the Golden Horn, towards the city.
A second channel, dating to the 5th century, was sourced much further to the west at Pazarlı, west of Vize, at Ergene, and near Binkılıç (now Fatih). This channel was 180km in length. East from Binkılıç it was normally 1.6m broad, and in places more than 2m high. In part, it ran parallel to but at a different elevation than the earlier channel. It remains uncertain whether the two channels continued separately as far as the city, since the evidence for the channels and bridges is less complete close to Istanbul’s urban sprawl. The combined length of these channels is 426km. There are 57 new bridges known from the second-phase channel, together with 11 newly built replacements along the first-phase channel, making a working total of around 100 bridges along the entire line.
Bridges from both phases vary in size. They range, according to need, from small, single-arched structures to majestic multi-tiered aqueducts rising to over 40m in height and spanning valleys up to 150m in length, like that at Kurşunlugerme. Five bridges of the second 5th-century phase rank alongside the monumental aqueducts of imperial Rome. In all cases, they replaced earlier structures, and in instances such as the new bridges at Kumarlidere and Büyükgerme, they replaced several smaller crossings with longer, higher structures and embankments that reduced the earlier, more sinuous route. The largest of these bridges was Kurs¸unlugerme. Set in a deep, forested valley, this structure remains one of the most dramatic survivals of late-antique Constantinople. Faced with metamorphic limestone ashlar blocks, which are almost like marble in appearance and hardness, its three tiers rise to a height of more than 40m. Christian symbols and texts decorate the vaults and keystones. It is a unique monument of the new city’s ambition and a Christian Roman Empire. The origin of this second monumental phase remains uncertain, although an earthquake in the region of the aqueducts at the very end of the 4th century may have accounted for the need to repair and replace the earlier bridges with much more substantial structures, as well as providing the impetus for the new extended line.
The work of construction was among the most outstanding infrastructure projects executed in the ancient world. It was an enormous undertaking, involving complex planning, surveying skills, and resource management. While the cost to the imperial treasury cannot be known, estimates based on length and construction materials give some idea of the magnitude of the undertaking. Stone required for the channels and the bridges amounted to just over 2.5 million cubic metres, a mass equivalent to the Great Pyramid at Giza. The quantity of mortar required was enough to fill 500 Olympic-sized swimming pools. Such enormous figures demonstrate the new city’s ability to command imperial resources in the 4th and 5th centuries, when Constantinople could rightly claim to be the New Rome.
But the story did not end there. The network was active over seven centuries, and, as we know from our own times, to remain effective hydraulic infrastructure requires maintenance and restoration. Major examples include making good the disruption caused by earthquakes and enemy action to the aqueduct bridges in the 6th and 8th centuries, but, more importantly, recent research on the carbonate samples from the western channels shows that they were kept free from the accumulation of calcium carbonate or sinter right up until the end of the long-distance system in the 12th century.
Water in the city
Constantinople itself grew westwards, with the new Theodosian land walls completed by c.415. This new intermural zone was never as fully urbanised as the city within the Constantinian walls, with much of it given over to elite houses, monasteries, parks, and horticulture. Shortly after the completion of the new walls, the Cistern of Aetios – now occupied by a minor league football stadium – was constructed in 421. It was the first of three great open-air reservoirs excavated in the intermural zone. Although there is no direct evidence, it is difficult not to associate this new reservoir and the other two, the Mokios and Aspar cisterns of the later 5th century, with the additional provision of water made available by the new long-distance line from Vize. In total, these reservoirs could have held more than 600,000m3 of water. While these new resources could have contributed to the agriculture and gardens of the intermural zone, they are best seen as the city’s strategic reserve, not only in times of war and crisis, but also with respect to the management of water-distribution across the city.
The city’s aqueducts passed through the northern end of the land walls at two elevations. Neither point of entry survives today. The elevation of the upper line can be determined from the surviving height of the 971m line of the Aqueduct of Valens. Stone pipes discovered during roadworks beneath the modern streets follow the line of the Byzantine Mese and show this was a pressurised line in places. The lower Hadrianic line is known to have been the source of water for the Basilica Cistern or Yerebatan Saray, and the channel entered the city at an elevation of c.35m above sea level, comparable to the later Ottoman Kırkçes¸me supply line.
Cisterns are the most numerous surviving structures from Byzantine Constantinople. Cut into the ground and lined with waterproof hydraulic mortar, they survive in a range of locations, reused as (among other things) restaurants, marriage venues, shopping arcades, and hidden storerooms. They vary in size from the massive open reservoirs located in the intermural zone, large covered cisterns like the recently restored Basilica Cistern, and the many smaller cisterns providing water for individual dwellings. Although the smallest may have benefited from rainwater collection, the majority were part of the city’s water supply and distribution network. Recent research has identified over 210 examples, including those first documented in the 19th and early 20th centuries. The preponderance of cisterns occupies the higher ground in a band north of the Valens aqueduct and, from there, they are more or less uniformly spread across the east end of the peninsula, especially on the city’s First Hill, later occupied by the Topkapı Palace.
Historically, cisterns were constructed in the city from the 4th century onwards. Anastasius (491-518) may have introduced large, covered cisterns to the heart of the city with the Binbirdirek or 1,001 Columns Cistern and the Cold Cistern at the west end of the Hippodrome, although the chronology of these is not certain. As the deepest of the large urban cisterns, the Binbirdirek reflects the need to create a vast storage space with a limited footprint in what was a crowded urban region. Soon afterwards, Justinian (527-565) constructed the Basilica Cistern below the courtyard of the pre-existing Basilica, opposite the newly rebuilt church of Hagia Sophia. The largest of the covered cisterns, it had a capacity of 80,000m3 and is a massive example of urban infrastructure, with its brick vaults supported on an array of columns often capped by decorated capitals using stone from the nearby island of Proconessos in the Sea of Marmora. The apparently redundant and enigmatic elaboration of its structures far exceeds even the grandest of the imperial Roman cisterns in both scale and design innovation, reflecting the value of water in the Byzantine city.
Learning from the past to inform the future
A new project ‘Water in Istanbul: rising to the challenge?’, supported by various funders, is now bringing together archaeologists, engineers, social scientists, and historians from Edinburgh and Northumbria Universities, Istanbul Technical University (ITU), Middle East Technical University (METU), and the British Institute at Ankara (BIAA) to investigate the water-management infrastructure of Istanbul at two key phases in the city’s life – the transition from Byzantine to Ottoman rule, and the much more recent period of massive population explosion beginning c.1980. The new project continues the collaboration with engineers and archaeologists by modelling the water distribution on the ancient acropolis – now the site of the Topkapı Palace – and builds on previous research to explore how past practices can inform solutions to contemporary water-related challenges. A decade ago, our colleague Çiğdem Özkan-Aygün from ITU explored the tunnels and wells below Hagia Sophia with assistance from the Anatolian Speleology Group (ASPEG). In addition, they investigated underground features in the Hippodrome and cisterns within the Topkapı Saray. Throughout the 70ha defined by the circuit wall of the palace, 28 underground cisterns of various sizes have been identified: the densest distribution of cisterns known from the city. The Ottoman palace occupies a high, separate hill, posing particular challenges for water distribution based on gravity. Byzantine and Ottoman buildings and water features are contextualised and analysed using GIS tools, which forms the basis for ongoing engineering modelling to explore past practice and innovation.
One of the main ways in which learning from the past can inform responses to contemporary challenges is through engagement with those responsible for the modern water-management infrastructure of Istanbul, to share insights from the archaeological fieldwork and hydraulic analysis, identify current challenges, and discuss potential solutions. Three participatory knowledge-generation workshops – attended by more than 70 representatives from the Istanbul Water and Sewerage Administration (ISKI), Istanbul municipality, government agencies, and NGOs – have so far been organised to explore this topic. The workshops presented aspects of the historic water-management infrastructure, explored current needs, and examined rainwater-harvesting and water-storage from legal, technical, and social perspectives.
The historic water-management theme found to be most interesting to these stakeholders was rainwater-harvesting, and a final workshop discussed its use on a neighbourhood scale as a means to create new water supplies for common public use, such as park irrigation and street washing. The history of water use in Constantinople/Istanbul shows great determination and adaptability in past generations, offering potent examples for contemporary water-managers to meet the demands of the present and the future city.
PHOTO: Dreamstine/Mehmet Cetin
We wish to thank a number of funding agencies for their generous support. The Leverhulme Research Trust funded two major grants (1999-2004, 2014-2017), AHRC and the British Academy provided additional funding, and the British Institute at Ankara (BIAA) gave critical administrative help and funding for more than 20 years. In Turkey, TÜBI.TAK (National Funding Agency) sponsored our collaboration with Istanbul Technical University (2007-2009). The current project (2021-2023) is funded by the British Academy’s Knowledge Frontiers: International Interdisciplinary Research scheme, BIAA Research Grants, the Scientific Research Projects department of Istanbul Technical University, and the GCRF Fund of the University of Edinburgh.
Recent publications include: J Crow, J Bardill, and R Bayliss (2008) The Water Supply of Byzantine Constantinople (London). K Ward, J Crow, and M Crapper (2017) ‘Water supply infrastructure of Byzantine Constantinople’, Journal of Roman Archaeology 30: 175-195. J Crow (2022) ‘Waters for a capital: hydraulic infrastructure and use in Byzantine Constantinople’, in S Bassett (ed.) Cambridge Companion to Constantinople (Cambridge), pp.67-86. Kerim Altuğ (2022) Arkeolojik Gezi Rehberi: Yeraltındaki I.stanbul (‘An Archaeological Guide: underground Istanbul’; Istanbul Büyüksehir Belediyesi).