Revealed: The long lost secrets of the ancient world’s second Rome

David Keys explores how British and Czech archaeologists have been solving the mysteries of Roman Constantinople

Hagia Sophia today: Over the past 1500 years it has been a Greek Orthodox and Catholic cathedral, an Ottoman mosque, a museum - and again now a mosque (Getty)

British and other researchers have succeeded in uncovering the long-lost secrets of one of the world's most important buildings.

More than a decade of intensive investigations have revealed the original design and subterranean mysteries of Europe's largest ancient landmark – the former cathedral of Hagia Sophia in Istanbul, which for almost a thousand years was the largest conventional building in the world.

The research has, for the first time, revealed the layout of the original sixth century cathedral complex – and the existence of more than a kilometre of long-lost tunnels and subterranean chambers underneath the vast building.

The new discoveries are particularly important because, from a political and religious history perspective as well as an architectural one, Hagia Sophia is one of the most significant buildings in the world.

It was originally built to symbolise the establishment of a political philosophy which still dominates parts of the world today – namely the unity of church and state, the merging of ideological and political authority.

Hagia Sophia was constructed as a powerful symbol of that political concept – and the more unified form of government it's builder, the late Roman (early Byzantine) emperor, Justinian, imposed.

Justinian, one of the greatest of Roman emperors, built Hagia Sophia and imposed his more centralized political system just two generations after the western European part of the Roman Empire had collapsed, leaving just south-eastern Europe and parts of the Middle East under imperial control.

As a result, Justinian's newly invigorated governmental system shaped aspects of subsequent East European history in ways that did not occur in Western Europe, where church and state became much more separate and politics consequently evolved in more pluralistic and less centralised ways.

The new discoveries at Hagia Sophia show that Justinian's great cathedral was part of a much larger complex of buildings at the heart of the late Roman (Byzantine) imperial capital, Constantinople (now Istanbul) - often dubbed 'the second Rome'. Prior to the investigation, apart from the cathedral itself, there was physical evidence for just two major structures on the site.  

However, British-and-Czech-led archaeological survey work has revealed that there were at least five, including Hagia Sophia itself.

The newly re-discovered buildings include:

- The great palace that Justinian built for the most senior official of his empire's church, the Patriarch of Constantinople.

- The Great Baptistery – the sumptuous building where Justinian's successors had their children (often future emperors) baptised.

- The Patriarchal Council Chamber – where some of Christianity's most important theological and other decisions were taken (including the historically very significant decision to increase the religious status of the Virgin Mary). The same building also housed the great library of the patriarchs.

The archaeologists also discovered nine 6th century frescoes, two mosaics - and the previously unknown great north-western entrance complex of the cathedral.

"Our long and detailed investigation has, for the first time in more than five centuries, revealed physical evidence of how Hagia Sophia was part of a larger complex of high status religious buildings at the heart of the Byzantine imperial system," said the co-director of the research project, Professor Ken Dark of the University of Reading.

"Indeed, Justinian's great cathedral was constructed as the physical representation of the religious and political ideology of his empire,"  said Professor Dark, co-author of a major book on the building, Hagia Sophia in Context.

The archaeological survey has also, for the first time, established how secular imperial power was actually integrated into Hagia Sophia's spiritual rituals. In a seldom-visited part of the cathedral, the archaeologists discovered a 59cm diameter purple marble disc where the Emperor Justinian and his successors used to stand at key moments in religious services.

It's now thought that there was a whole series of such imperial purple discs (each made from purple marble imported from an Imperially-owned quarry in Egypt) at key locations across the cathedral. They seem to have marked the route taken by successive emperors as the Patriarch recited the liturgy – a bit like imperial equivalents of the Stations of the Cross.

The investigation also discovered, for the first time, that Justinian had clad his great cathedral in glistening white marble – so that it would shine and shimmer in the rays of the sun. In both Roman and Greek traditions, white symbolised purity.

The new discoveries show how Hagia Sophia was constructed to quite literally shine over the imperial capital. As Justinian, established his new political system, unifying church and state, he seems to have been determined to embed the church at the heart of Roman/Byzantine imperial state identity in a way that never occurred politically in the West.

Analysis of the new discoveries - especially the previously unknown frescoes -  is still continuing, as is an analysis of recently discovered inscriptions written by the ordinary workmen who built the cathedral almost 1,500 years ago.

Separately from the British-and-Czech-led archaeological investigation into Hagia Sophia, Turkish researchers have been discovering how the Romans had built a huge network of tunnels and chambers underneath the cathedral.

Most of this long-lost subterranean network is now filled with water – and has had to be explored by teams of divers.

It is now estimated that there are more than a thousand metres of tunnels and hidden rooms under Hagia Sophia – although most of them have not yet been explored.

Archaeologists believe that some were used as water storage cisterns, while others may have functioned as underground chapels and burial areas.

Water would have been crucial to the functioning of Justinian's great cathedral complex – partly because of the need to irrigate probable ornate gardens and sustain its once spectacular fountains.

Justinian's Hagia Sophia Cathedral was born out of a huge political crisis which almost toppled the emperor. Its construction symbolised the ambitious nature of the re-establishment of his power.

In Roman Constantinople, there was intense and often very violent rivalry between the supporters of the two main teams of charioteers – civil discord that makes modern football rivalries look mild in comparison.

What's more, the two charioteer team fan bases had different political identities and aspirations. One was relatively pro-establishment, while the other one was much less so.

Around five years after Justinian came to the imperial throne in AD 527, that rivalry ultimately generated an attempted revolution in which much of central Constantinople (including the city's cathedral) was burnt to the ground and a new anti-Justinian emperor was proclaimed and crowned by the rioters.

After initially preparing to flee the capital, Justinian (encouraged by his very remarkable wife, Theodora), decided to ruthlessly suppress the revolt. Some 30,000 rioters and others were slaughtered – and Justinian decided to establish a much more autocratic form of government, unite church and state and create a brand new mega-cathedral, built on new revolutionary architectural principles.

The new Hagia Sophia (literally, 'Divine Wisdom') was in several ways unlike any other building ever constructed in the ancient world.

First of all, it enclosed an unprecedented amount of space – some 175,000 cubic metres.

Secondly, it had and still has a vast roughly square floor – covering some 5200 square metres of open space.

Now, for the first time, the archaeological investigations have allowed scholars to understand just what Justinian's great cathedral looked like – and precisely how massive and politically important it's complex was.