While Istanbul has witnessed all sorts of salvage archaeology in the past century, there has been virtually no urban archaeology – that is, rigorous excavation to determine the basic features of the city, such as the street system, public spaces and housing, all of which remain poorly understood. Our view of the Byzantine city is consequently limited to discrete churches devoid of context, which present at best a distilled essence of the city’s historic greatness. For most of us, Constantinople seems more a concept than a reality. We have lots of isolated monuments, and even more broken bits, but we lack the big picture – so in a form of synecdoche, we know the city through its parts.

How then to envisage the big picture of Constantinople? Start with the churches. Nothing can replace the experience of Ayasofya’s (Haghia Sophia’s) immense spaciousness (page 148) or the intimate, jewellery-box quality of the Church of the Chora (which became the Kariye Camii and is now a museum, page 154). These two churches represent the yin and yang of Byzantine art and architecture. In spite of the ups and downs of scaffolding (finally down last year, up again this year), Ayasofya remains justifiably the most popular museum in the city, and an engineering achievement without rival.

In contrast, the Kariye is as intimate as the Ayasofya is grand. Its mosaics and frescoes still enchant with their odd combination of intellectual rigour and aesthetic refinement. Few images can rival the dramatic Angel of the Lord Rolling up the Scroll of Heaven at the End of Time in the funerary chapel.

But don’t stop there – visit some of the B-list churches as well, all of which survived as mosques. Ayasofya’s immediate predecessor, the church of Sts Sergius and Bacchus, now Küçük (Little) Ayasofya (page 160), is as spatially sophisticated as its namesake, with a dome half its diameter. Although it preserves no mosaics, its architectural sculpture is stunning, its geometry complex. Similarly, the funerary chapel at the monastery of the Theotokos Pammakaristos (Fethiye Camii, page 168) is the immediate predecessor of the Kariye’s, with colourful brick and stone ornamentation on its exterior and animated mosaics in its diminutive interior. Much is missing, but the visages of craggy, bearded monks crowded into the corners make it worth the visit. Painstakingly excavated from 1966 to 1978, the Theotokos Kyriotissa (Kalenderhane Camii, page 164) preserves a fine array of marbles in its spacious interior.

Not interested in churches? Recent research on the water system has shed new light on daily life in Constantinople. While less glamorous than a decorated church, the arcaded Aqueduct of Valens – after the Roman Emperor Valens – is impressive, representing a fraction of the 592-kilometre system of channels that brought water into the city (page 84). Once inside the walls, water was stored in dozens of cisterns, many built into the substructures of major buildings. The Basilica Cistern (Yerebatan Sarayı, page 66), across the street from Ayasofya, once supported the courts of law, now vanished. Tourists stare at the forest of damp, drippy, mismatched columns and ponder how the marble head of Medusa came to be stuck upside down in a far corner, but none of this was ever here for show; the marbles are simply remnants of the monumental public buildings upstairs.

The other introductory synecdoche I recommend is the excellent Istanbul Through the Ages display in the Archaeological Museum. Try this approach: first examine the evocative broken bits on show, paying close attention to the information on the wall labels, then track down the findspot. Let the art lead you into the city.

For great cities size matters, and for cities like Byzantine Constantinople, almost totally obscured beneath the Ottoman and modern city of Istanbul, the scale of the past glory is rarely glimpsed through the majesty of monumental buildings such as Justinian’s Ayasofya, and from the relics of the imperial hippodrome, the Land Walls and the recently excavated Theodosian harbour at Yeni Kapı. To appreciate the Byzantine city requires effort and imagination.

Astride one of the old city’s main boulevards, like a comb parting the constant lines of traffic, the multi-arched Aqueduct of Valens (Bozdoğan Kemeri) is among the longest Roman aqueduct bridges known, only 29 metres short of a full kilometre in length. Built in the 4th century to carry water from the fourth to the third hill of the city, it is the most obvious surviving element of the new water supply system constructed for the expanding metropolis. This was the vital link for water to flow towards the Forum of Theodosius, where there was a great fountain, and from where water channels led throughout the new city, terminating at the huge underground cistern of a Thousand and One Columns (Binbirdirek). The better-known Basilica Cistern (Yerebatan Sarayı) was built by Justinian but filled by the Hadrianic aqueduct. At least 170 cisterns are known from the Byzantine city. Many are far smaller, but others located towards the Theodosian Walls were vast open-air reservoirs later used as market gardens, playgrounds or football stadiums. Strange as it might seem, the remains of water systems far exceed any other category of surviving monument known from the Byzantine city.

Where did this water come from, and how was it channelled? For the past 20 years Turkish water engineers and British archaeologists have been investigating the sources and courses, with some amazing results. Constantinople was the largest city in the ancient world by the 5th century, and the network of channels and bridges in Thrace stood comparison with the 11 aqueducts of ancient Rome.

If, as the saying goes, God is in the detail, then historic preservation is a divine occupation. It follows that the best practitioners approach their work with a missionary zeal. As with any religion, there is the right way, or no way at all. Compromise and haste, usually products of a treacherous conspiracy involving politicians and contractors, are the cardinal sins of historic preservation, which can threaten the very soul of the monument in question. Working on the restoration of the Zeyrek Camii in Istanbul over the past decade has made me a convert.

I have spent much of the past five years on the roof of the Zeyrek Camii. It was a mess, but the view was fabulous. To the east, the panorama spans the Aqueduct of Valens to the Süleymaniye Camii, to the Golden Horn and Galata. To the west, the view is dominated by the Fatih Camii and the Selimiye Camii. Closer at hand are the remains of a dilapidated neighbourhood of wooden houses and the foundations of an Ottoman konak now converted into an upscale restaurant. It is easy to get lost in the view and forget that beneath one’s feet was one of the most significant and threatened monuments in the city’s history.

For the English-speaking community of Istanbul the suggestion of aqueduct-hunting in Thrace strikes fear into the hearts of all but the foolhardy. For years, tours by the Friends of the American Research Institute seemed cursed to lose their way (as a group or individually), get stuck in the mud (usually by the busload), fall into the river (usually individually), or at the very least get rained on (without exception). Relentlessly cheerful, Prof James Crow of Edinburgh University (mastermind of both the tour and this book) would laugh off each misadventure and forge onward.

Within a few dozen kilometres of Istanbul, Thrace transforms into an inhospitable jungle – sparsely inhabited, densely vegetated, seemingly unworthy of the historical epithet “hinterland of Constantinople”. To the untrained eye, there is virtually nothing of interest there. To the valiant British aqueduct-hunter, however, Thrace is a gold mine, as this book lucidly demonstrates.

Hidden beneath lush foliage and tucked away in deep, uninhabited valleys lie the remains of the world’s longest ancient aqueduct system, which supplied the early Byzantine city of Constantinople with copious quantities of water. By Crow’s calculations, it measured 592km in overall length, surpassing the total length of Rome’s 11 aqueducts by some 72km. Constituting one of the greatest engineering feats of the ancient world, it was essential to the existence of the Byzantine capital, which was strategic geographically but lacked a good source of water within its walls. Thus writing the history of the aqueduct system means in effect rewriting the history of the city.

For the uninitiated, the term aqueduct conjures images of postcard-worthy, multi-tiered, arcaded bridges, like the Pont du Garde in southern France. Indeed, the almost 1km span of the Aqueduct of Valens (the Bozdoğan Kemeri) in central Istanbul comes closest to fitting the bill. But Roman aqueducts were utilitarian rather than aesthetic achievements, designed to provide water to a thirsty city and not necessarily to elicit oohs and aahs from passing tourists. In fact, most aqueducts avoided bridges whenever possible. The point was to create a near-level channel through which the water could flow gently from the springs in the hills to the cisterns, fountains, baths and nymphaia of the city. As Crow explains: “The normal option was to construct the water channel against the side of the hill so that the line proceeded, often with great sinuosity, around the hills in order to maintain a gentle gradient toward the city.” With this “cut-and-cover” method of construction, most of the aqueduct consisted of buried channels; only when the vagaries of the topography dictated was a deep tunnel or arched bridge included. Like their Roman predecessors, the early Byzantines were pragmatic, and, while a grandiose bridge might testify to dominion and territorial control, it was more important to provide the capital with water.

Fortunately there are a small number of picturesque bridges. A few summers ago I joined the intrepid team for a day of aqueduct-hunting, armed with camera and umbrella. They came armed with topographical maps of eastern Thrace and hand-held GPS units, for they had become familiar enough with the water system to be able to predict when an aqueduct bridge should appear. As they had determined, once the position and relative elevation of a spring had been identified, it remained to chart the path of least resistance – that is, to follow the lines of the topography in a gentle descent into Istanbul. Evidence from exposed channels and tunnels provided additional clues. The jungle-like plant growth argued against free-range exploration, but local farmers, charcoal-burners and curious boys provided tips on the locations of surviving components, which often were romantically misnamed. On the day in question, both the system of prediction and a local farmer had indicated that a hike up the Kale Dere stream would bring us to the remains of a bridge (in local lore, however, it was a castle).

After a mercifully short bout of machete-hacking at the foliage, the bridge appeared – to no one’s great surprise except possibly my own – exactly where it was supposed to be. Spanning the deep gorge, the bridge connected to buried channels on either side. Working with the relative elevations allowed the team to rewrite the history of the city’s water system, both outside and inside the city walls. For years the common opinion had been that the Bozdoğan Kemeri represented the sole provider of water for the city, and that it was Emperor Valens’s fourth-century rebuilding of a system introduced by Hadrian in the second century. But the historical references were often contradictory, and the numerous surviving cisterns within the city are on several different levels.

The authors determined that there were in fact two lines of aqueducts. The earlier, Hadrianic line preserves no spectacular bridges but followed the topography from near Cebeciköy into the city along the Golden Horn at an elevation of 30–34m above sea level.

Water channels have been found at that level within the walls, and this line would have supplied the forum of the old city of Byzantion, as well as the Basilica Cistern, the Baths of Zeuxippos and the Great Palace. As the population grew and the city expanded, more water was needed, and the Valens system was added in the mid-fourth century, extending deep into the hills of Thrace. It entered the city at a level over 20m higher than the older system, and provided water to the higher elevations of Constantine’s new city. The Valens system was subsequently expanded westward as far as Vize, and the great open-air cisterns were added inside the walls of Theodosius, primarily to supply water for agriculture.

The resulting book provides a valuable synthesis of archaeological and historical data that no well-equipped research library should be without. In addition to tracking the water channels, bridges, tunnels and cisterns, the book also catalogues all historical texts (in translation) related to Constantinople’s water system, inscriptions, masons’ marks and Christian symbols, as well as documenting the repairs and maintenance of the system through the centuries.

While the general reader may be swept away in the wash of too much information, the specialist will bathe happily in the careful documentation that follows a decade-long process of discovery and analysis. Ironically, exploration began as a study not of the water system but of the city’s defenses, tracking the line of the Long Wall, the outermost line of fortification that lies some 60km west of the city. Supplementing the Land Walls of Theodosius II, the Long Wall was built circa 500 by Anastasius and extended from the Black Sea to the Sea of Marmara.

As Crow and Co quickly realised, the two systems were inextricably linked: the protection of water sources was critical to the city’s survival. Now that the definitive book on the water system has appeared, we eagerly await the final publication on the Long Walls.