From soldiers to saints on the Caelian Hill

Within the labyrinth of tunnels that spreads out from under the Basilica of St John Lateran are remarkable traces of structures that ended up entombed beneath the world’s first cathedral. The walls of elite houses, such as that pictured, still have fragments of frescoes clinging to them.

Today, a network of subterranean passages spreads out from under the world’s first cathedral, in Rome. Within the tunnels are remnants of Roman buildings dating from the Republic to the 4th century AD. The challenges associated with piecing together this remarkable jigsaw puzzle mean that the remains have never been studied as a group, until now, as Ian Haynes told Matthew Symonds.

Despite its name, the Arch of Constantine in Rome presents viewers with a collage of art created under several emperors. Crowning the columns are statues of Dacians with their heads bowed, subdued by defeat at the hands of the emperor Trajan, two centuries earlier. Below them, the emperor Hadrian hunts and sacrifices, his features diplomatically reworked to resemble Constantine. While the inscription dominating the monument leaves no doubt that this vigorous medley was assembled in honour of Constantine, following the destruction of a ‘tyrant and all of his followers’, the genuine Constantinian art is easily overshadowed by its predecessors. The most striking piece commissioned for the arch itself is a frieze illustrating Constantine’s victory over the ‘tyrant’, otherwise known as the emperor Maxentius, at the Battle of the Milvian Bridge in AD 312. One panel depicts the brutal denouement to this clash, with Maxentius’ forces drowning in the Tiber, while Constantine’s soldiers stab at them. The destruction of Maxentius’ army did not just furnish Constantinian artists with some much-needed inspiration, though, it also changed Rome forever and paved the way for the world’s first cathedral.

Today, the Arch of Constantine lies just over 1km from the Basilica of St John Lateran on Rome’s Caelian Hill, but despite this proximity, few tourists venture up the slope. As a result, the church rarely attracts crowds to equal those milling around the Arch as they amble from the forum to the Colosseum. After all, visitors eager to experience ecclesiastical architecture typically congregate at Vatican City, where the splendour of St Peter’s awaits.

The Arch of Constantine was erected to commemorate his victory over the emperor Maxentius at the Battle of the Milvian Bridge in AD 312. Much of the artwork was ingeniously recycled from earlier monuments, with the
two scenes in the roundels showing the emperor Hadrian hunting and sacrificing. Underneath, though, is a genuine piece of Constantinian art, which depicts Maxentius’ forces drowning in the Tiber as Constantine’s victorious soldiers hack at them.

Long before St Peter’s rose to supremacy, Constantine viewed the summit of the Caelian Hill as the perfect venue to offer his new vision for Rome. It was there, beside the major Via Tusculana highway, that Constantine founded the first cathedral, ensuring that the centrepiece of the city’s new Christian architecture dominated the skyline as travellers approached from the south-east.

Constantine did not raise his basilica on virgin ground, though. Instead, housing had long since developed on the Caelian Hill, which had even been exploited once before by an emperor looking to make a statement. Extraordinary traces of this shifting urban fabric can be still be found in a bewildering network of tunnels stretching out under the Lateran basilica. To make sense of this archaeology, the Lateran Project was set up in 2012, and is drawing on the talents of Newcastle University, the Università degli Studi di Firenze, the Musei Vaticani, and New Visions.

Subterranean secrets

‘There is a large area of space underneath the Lateran that it is possible to walk or crawl through,’ explains Ian Haynes, Professor of Archaeology at Newcastle University and co-director of the project with Florence’s Professor Paolo Liverani. ‘Although these passages are connected, they were opened as a result of multiple different interventions. Some of the earliest date back to the 19th century and were primarily non-archaeological; others were driven by antiquarian interest, and some were pretty sophisticated archaeological appraisals. But, as was the spirit of the day, they tended to focus on the structural remains. As a result, a lot of the artefacts – which in fairness were probably mostly from back fill – were not recorded in context. So, we’re dealing with multiple different excavations undertaken by multiple different players, over the course of several centuries. Even when the individual findings were analysed, it was done in a disjointed way, because there was no way to tie all of the exposed archaeology together. Our project is the first ever attempt to undertake a holistic analysis of the whole lot. We’re achieving that through minimally invasive work, so we’re not generally digging; it’s more a case of integrating the results of standing building survey, laser scanning, and ground penetrating radar (GPR).’

Accessing the archaeology requires techniques and kit more commonly associated with potholing.

Undertaking a comprehensive survey of the ruins visible within the warren of tunnels presents challenges more commonly associated with potholing than archaeological fieldwork. ‘It does require spending a certain amount of time in hot, tight, and uncomfortable places,’ Ian says. ‘In some places it is necessary to rotate the teams on a half-hourly basis, because otherwise it just becomes stifling. Other places, I should say, are completely fine. To access some of the spaces we work with a group called Roma Sotterranea, who specialise in working on buried sites and use exactly the same equipment – and often exactly the same techniques – as pot-holers. The difficulty involved with reaching some of the sites has also influenced our recording techniques, because filming video diaries becomes particularly valuable when it’s only possible to squeeze one person and a camera into a space. The quality of some of this subterranean archaeology is extraordinary, but large parts of it are only ever accessible to members of the Lateran estate service and determined archaeologists!’

‘There are various ways of calculating the amount of area we have scanned, but it is perhaps easiest to say that the site runs over 4.167ha, which is the equivalent of seven Wembley Stadium football pitches. Of course, that area is not just as a flat pitch: that’s with all of the archaeology at varying levels below it. At deepest, we are 8.5m below modern ground surface, so there really is quite a range, and this approach lets us virtually remove all of the earth to see the precise spatial relationship between the different structures. Laser scanning allows us to record to sub-millimetre accuracy, so our data-sets are big enough that if a standard computer tried to process them it would just fall over! We’re also doing work above ground, because everything we’re recording needs to be locked into archaeological and historic fabric visible on the surface.’

The team, including co-director Ian Haynes (above), are required to delve through subterranean spaces and passages dug for varying reasons that differ considerably in size.

Wealth, warriors, and worship

Combining the information from this high-tech surveying allows the biography of a remarkable patch of Rome to be told. In many ways, it is a story that revolves around the sweeping vistas over the metropolis available from the Caelian Hill. As well as finding favour with the elite, this setting proved to be the perfect venue for two emperors looking to shore up their power base by securing a dominating position within Rome for two very different institutions. The result was an area of the Eternal City that became home to a distinctive community, where the range of people present periodically shifted in line with wider imperial priorities. What the existing homeowners made of these makeovers is a different matter, but they certainly seem to have taken the changes in their stride, as archaeological work in the wider area is revealing elite residences that continued with little evident disruption.

The earliest of the walls that are visible beneath the Lateran can be dated to the Republican period. ‘We see the remains of elite residences,’ says Ian, ‘which were built on the natural slope of the hill. “Elite” is of course exactly the sort of ambiguous term that archaeologists love using, but the people living here were clearly very wealthy indeed. The quality of the surviving wall plaster, for example, stands direct comparison with imperial palaces on the Palatine Hill. Ornate stonework has also been created to the very highest standard. Following the emergence of the empire, it seems safe to say that these would be people who were in the imperial circle. Over time, the properties change and develop, with one group of buildings seemingly combined into a single residence and redecorated in the contemporary fashion during the Hadrianic period. One of my favourite fragments of early wall initially appears pretty unprepossessing, but when you look at it closely, you can see holes to support marble cladding to a height of about 6m. It must have been extraordinarily elaborate. The other notable thing about this wall is that it is enclosed within the brickwork of a later structure, which was built on a completely different alignment. These are the foundations of a major new structure that transformed the site early in the reign of the emperor Septimius Severus.’

A radically reduced two-dimensional image derived from the project’s full-size digital model of the Lateran excavations and Basilica interior. The model, generated by laser-scanning survey, facilitates the investigation of relationships between different parts of the complex’s vast interior.

Severus was born in Leptis Magna, in modern Libya, and reigned from AD 193 to 211. Today, Severus is most famous as a soldier-emperor who came to power through civil war, and died after falling ill while campaigning in Britain. Severus himself, though, took pains to create another legacy, one that is often eclipsed by his devotion to military matters. A few years earlier, fire had swept through Rome, devastating the region between the Temple of Peace and the Palatine. This provided Severus with an opportunity to become the most active embellisher of the capital since the emperor Hadrian over half a century earlier. It was a role that Severus embraced with gusto, and a coin issue of AD 200-201 acclaimed him restitutor urbis – restorer of the city – placing this boast at the heart of his propaganda campaign. One of the remarkable features of the Lateran tunnels is that they provide a glimpse of what happened when the two sides of Severus’ personality combined.

Despite Severus’ eagerness to style himself as a ‘restorer’, he was not afraid to destroy buildings that stood in the way of his vision for Rome. A couple of the old Republican residences on the Caelian fell into that category, because they occupied the plot earmarked for a new stronghold to house the emperor’s horse guard: the equites singulares. It was this military base – called, prosaically enough, the Castra Nova or new fort – that the brick foundations straddling the former marble-clad wall were constructed to support. This monumental platform swept away not only earlier buildings, but also the natural contours of the hill, creating a jarring new local topography. Those occupying the houses that survived this radical reworking suddenly found themselves living next door to soldiers who had been brought up in distant lands.

The changing alignment on the Caelian Hill. The earlier walls of an elite residence with traces of frescoes still attached are contained within the grid-like walling of the Severan platform supports, as captured by the team’s laser scanning.

‘The Caelian has been described as a Roman Beverly Hills,’ says Ian, ‘but we know that lavish houses existed adjacent to this new military landscape throughout its life, so perhaps it’s better to think of it as more like Knightsbridge in London. There, too, you have very luxurious houses juxtaposed with elite guards. It’s interesting to think about how that works as a community. The extra horse guards weren’t the only troops that Severus introduced to Rome, though. During this period the overall military presence in the city appears to have doubled. What’s more, at the same time that the Castra Nova was being established, a full legion – the II Parthica – was brought to the Castra Albana, just 20km away. What we are seeing is the military grip on Rome tightening, and therefore the nature of Rome itself changing. The men making up the horse guard certainly made an impression, and the ancient author Cassius Dio describes these “motley soldiers, most savage in appearance, most terrifying in speech, and most boorish in conversation.” You get the sense that Dio wouldn’t have been great at parties! But what he is picking up on is that these soldiers brought alien habits that would be familiar on the Danube, but were decidedly not something that Rome welcomed.’

Another military habit that might have left polite society frowning can be found on the walls of the former houses entombed beneath the Castra Nova platform. The fine frescoes still clinging to the brickwork offered a canvas for graffiti that proved too tempting for the construction teams to ignore. In many cases their handiwork amounted to no more than adding personal names, but in one instance ‘COH III’ was scratched into a brightly coloured panel. This reference to a cohort betrays the presence of infantry rather than the cavalry making up the equites singulares, revealing that the elite horse guards did not deign to build their own fort, and another unit was brought in to do the dirty work. Sadly, another and more imaginative doodle only survives as a photograph in a 1930s photo archive. It seemingly depicts an ostrich hunt in the Colosseum, with the ill-fated bird shown falling backwards with its wings outstretched. Construction of the fort itself continued apace and an inscription reveals that a schola curatorum was operational in the fort headquarters building by 1 January 197, less than four years after Severus came to power. Such swift work testifies to Severus’ determination to install the unit within the city.

This reconstruction of one of the offices within the headquarters building in the Castra Nova is based on the surviving traces of wall plaster and mosaic floor.

Important traces of the Castra Nova still survive on its artificial platform. ‘There are places where you can get up to Severan floor level,’ says Ian. ‘What “going up” means here is that you have to descend into the underground passages, and then literally with scaffolding and ladders climb back up and squeeze into relatively small spaces that are sealed between 1.4 and 2.1m under the modern cathedral floor. One area we can access is part of the fort headquarters building, where there are traces of burgundy wall plaster and mosaic floor. We’ve used this evidence to create a very realistic image of what one office in that complex looked like around AD 300. Outside, the central courtyard was probably decorated with green marble, so it’s not a subtle colour scheme. But then we are dealing with the imperial horse guards, and modesty was not really their thing.’

On the basis of the known structures, a tentative reconstruction of the entire military base can be proposed.

Mother of all churches

Ultimately, the departure of the equites singulares from the Caelian Hill proved every bit as dramatic as their arrival. They fought with Maxentius at the Battle of the Milvian Bridge in AD 312, and ended up among the helpless soldiers drowning in the Tiber that Constantine immortalised on his arch. While the destruction of the horse guards was judged sufficiently momentous to merit a rare piece of original artwork for Constantine’s triumphal monument, it also left the new emperor with the question of what to do about their old base. Constantine’s answer applied not only to the Castra Nova, but also a number of other sites associated with Severus’ militarisation of Rome: the land was given to the church. The Basilica of St John Lateran was founded on the platform installed for the Castra Nova, while the horse guards’ tombstones were recycled to build a mausoleum intended for Constantine, but eventually used for his mother Helena. Such actions powerfully symbolised that a new imperial Christian centre was rising phoenix-like from the ashes of Maxentius’ vanquished army.

Structural elements from Constantine’s cathedral reveal just how early what are now considered standard features were developed. The blocks found embedded in the Constantinian nave during the 1930s would
have been used as sockets for a liturgical grill, keeping the processional route to the altar clear. Its modern counterpart is still used in the Lateran.

‘The land may have been given to the church within weeks of the battle,’ notes Ian. ‘A decision was certainly taken pretty soon afterwards, and work on the Lateran started some years before it did on St Peter’s. To this day, the Lateran remains the seat of the Bishop of Rome, and in the 15th century it received the title of “head and mother of all the churches”. It is also a rare example of a church to have its own liturgical day, something that is normally reserved for saints. So, it is still a big deal. The cathedral was rebuilt in the 1650s, but there is still original Constantinian fabric in the walls, while the original foundations are exposed beneath the church. Indeed, the 17th-century work was undertaken alongside antiquarian curiosity about the church and a desire to retain and emphasise its Constantinian flavour. So even back then there was an interest in what the original church looked like. There have been various attempts to reconstruct it since then, and we wanted to pull all of this information together to create a digital cathedral that you can walk around.’

A digital reconstruction of the Lateran during Constantine’s day, showing the liturgical fence and featuring numerous sources of light that can be turned on or off to provide a sense of what visiting the world’s first cathedral was really like.

‘Working with our colleague Professor Lex Bosman, an architectural historian at the University of Amsterdam, and our superb visualiser colleague Iwan Peverett, we’ve incorporated information from earlier excavations, including one in 1937 that investigated objects embedded in the Constantinian nave. They are quite interesting from a liturgical point of view, because they show that during the Constantinian period there was not just the co-option of the basilica-form for use as a church, but also a redesigning of the interior space. In this case it was so that the presiding bishop could process undisturbed by the congregation up to the altar. We rediscovered all of this when we entered one of the voids under the cathedral and found the blocks exposed in 1937, which would have acted as the foundation for a kind of liturgical fence, bounding the central approach to the apse. Other clues came from material still in the church, including numerous marble columns and even some bronze ones that were probably originally cast in the 2nd century. We fed all of this into our digital cathedral, which is so detailed you can turn on and off every source of light from individual lamps. We also created a simpler model to test the acoustics and try to understand how sound would have worked in the basilica. That’s quite important when you think about how little we know about early 4th-century liturgy and how it might have worked.’ In that sense, thanks to the Lateran Project, we can still hear the echoes of Constantine’s Rome today.


The project is grateful to Dr Giandomenico Spinola, Vatican Museums Service; Mons. Natalino Zagotto, the Camerlengo of the Lateran Chapter; Soprintendenza Speciale Archeologia Belle Arti e Paesaggio di Roma. We would also like to thank the British Academy and the British School at Rome for their support throughout the research programme.

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