Digital techniques for heritage restoration

Palmyra’s triumphal arch was constructed in the 3rd century AD under Roman rule and was a good example of the fusion of eastern and western architectural styles. (Photo: Daniel Demeter).

Over the last decade, increased accessibility of novel digital modelling and recording tools has had a transformative effect on the theory and practise of architecture and civil engineering. The digital third dimension, once the reserve of specialist enterprises able to justify the significant cost of software and investment in the professional expertise required to make use of it, is now available to all. In the context of historic sites, buildings, and monuments, the impact of this democratisation has been extremely significant. Precise digital documentation tools allow cultural assets and their states of repair to be recorded economically with unprecedented accuracy and completeness; augmented reality models bring archaeological sites to life for the public; virtual reality models enable threatened structures to be studied remotely by professionals thousands of miles apart; and digital fabrication tools working in concert with computer models can be used for repair and reconstruction.

The last ten years have also, tragically, seen a growth in devastating attacks on architectural cultural property. Variously, for reasons of ideology, financial gain, or greed for power, extremist and militant groups have targeted archaeological and cultural sites across the world. While the destruction of the Bamiyan Buddahs by the Taliban in 2001 drew widespread outcry and criticism, it was not until 2015 when the long-time custodian of the Syrian archaeological site of Palmyra, Professor Khaled Al-Asaad, was murdered and the site decimated by extremists, that the issue received sustained attention in the mainstream western press and became a topic of visible public debate. Even then, it took some time for reasoned responses to the destruction of Palmyra’s monuments to catch up with people’s intuitions. Graphic images of the violence sparked horror across the world, but the world did not immediately understand why.

Initially, there were widespread attempts to try to account for the emotional response in scholarly terms. There was talk of the archaeological significance of the site, its age, the rebellions and aggressions of times past that the buildings had survived, and the technical accomplishments of their architects. It took time for it to be widely recognised that the reason the damage upset people so deeply actually had little to do with any of these things.

Taken at face value, ancient monuments are, to borrow from Francis Bacon’s 1605 book, ‘The Advancement of Learning’, no more than ‘history defaced’ or ‘remnants of history which have casually escaped the shipwreck of time’. We may be able to justify their inclusion in text books and museums solely as remarkable examples of ‘very old’, or ‘very rare’, or ‘very beautiful’ things – objects that inspire awe on account of their scarcity, having existed for a long time, or the craftsmanship that they embody. But they earn their place in our hearts by a very different route.

Physical heritage provides a vital backdrop to our human experiences and an anchor point for our personal and collective memories. Our shared experience of it helps to put the pattern of our lives in context and provides an important mechanism through which we can relate to others, individuals, communities, whole societies whom we may or may or not have ever actually met. Rather like a physical book is a repository for a set of ideas with which a community of readers form meaningful relationships, heritage objects are pan-generational repositories for spiritual and emotional glue – ties that bind people together across geography and time.

And so, attacks on cultural property are attacks not only on material realities but human ideals: it is for this reason that they move us to tears.

Since the destruction of Palmyra, a number of important digital-domain projects have been created, seeking in different ways to draw attention to the damage to the site and its importance to the people of Syria. Initiatives include a number of virtual reality modelling projects (see the New Palmyra Project, https://newpalmyra.org/), several digital archiving programs (see the Syrian Heritage Project, https://arachne.dainst.org/project/syrher), and a project to create a digitally-milled large-scale reconstruction of the site’s triumphal arch undertaken by the Institute for Digital Archaeology (IDA) (as discussed by Stuart Burch in ‘A Virtual Oasis: Trafalgar Square’s Arch of Palmyra’, published in the International Journal of Architectural Research, volume 11, issue 3).

The original triumphal arch was built in the 3rd century AD while Palmyra was under Roman rule. Architecturally, it is a beautiful example of the fusion of eastern and western styles for which Palmyra has long been admired: it is instantly recognisable as a Roman-style arch but it is decorated with the swirling foliage and flowers typical of ancient Persia. It was reduced to rubble in October 2015.

The IDA project employed advanced photogrammetry and a state-of-the-art 3D machining technique that allows digital computer models to be translated into physical structures using original materials – in this case, stone. The whole process, from the beginning of the digital modelling phase to the end of the construction phase, was completed in ten weeks.

In the first stage of the project, crowd-sourced photographs of the original arch, taken prior to destruction, were used to create a three-dimensional digital model. Continuing in software, this model was then solidified and transformed into an engineering assembly comprising seven individual parts interlocking through a system of concealed steel pins. Each of these parts was then machined from a solid block of Egyptian marble by project partners Tor Art using robotic equipment adapted from that used on automotive assembly lines.

The finished structure is 18 feet high and was first unveiled on London’s Trafalgar Square by the then mayor of London Boris Johnson and the then director general of antiquities and museums in Syria, Maamoun Abdul Karim, on April 19, 2016.

The arch attracted large crowds in London, but more significant than the foot-traffic alone was the extent to which the people of London welcomed it as a means to express collective solidarity with the Syrian people. The arch began to take on a life of its own as a kind of monument in its own right – a symbol of hope over despair and of cooperation over conflict.

Five months after the London installation, the structure was erected on New York City’s City Hall Park. The arch then travelled to Dubai in February 2017, followed by Florence in March for the G7 Culture Summit. It then spent the summer in the Italian town of Arona where its installation was organised as a tribute to Khaled al-Asaad, and it was then installed in September 2018, on the National Mall in Washington DC.

Three years into the project, almost 3 million people had visited the arch in person and hundreds of millions had seen the installation through television, radio, and print media coverage. Against this backdrop, it is interesting to ponder why the project has so powerfully captured the public imagination.

The reason, perhaps, takes us back to the question of the real meaning of cultural heritage to real people. This project is one that has been made possible by ingenious digital techniques, but the structure that has been created is far more than a technological proof-of-concept for a new way of building things. The arch is not an attempt to replace an original structure, but rather a substrate for the formation of new relationships that reference it. For some, it provides a means to reconnect with, or resurrect, their personal relationships with the original object. For those with no personal connection with Palmyra it has meaning as a symbol of support for a shared understanding of humanity, history, and heritage.

Although the practical implementation of the work might be reduced to a concept for the reversal of physical damage to physical things – for their restoration or reconstruction – this is not a project that’s activities can be summed up solely through some variety of technical assessment. Rather, it is about an exploration of restoration in a much broader sense.

The project of supporting communities that have suffered as a result of cultural cleansing or the large-scale devastation of physical heritage, however wrought, is not just about the practical challenge of rebuilding physical things. It is about restoring people’s connections with each other and with their history and their culture, through the act of the reconstruction of physical things. This means that the success of any project that references the restoration or reconstruction of heritage objects and architecture should be measured not only by the impressiveness of the technology that makes it possible – crucial though that is – but in the extent to which the process of reconstruction enables people or peoples to retain or reclaim the sense of individual and community identity invested in what is being rebuilt.

Digital techniques open doors to some exciting opportunities in the context of heritage restoration and protection but they find their greatest and highest use not as instruments of progress for its own sake, but in the service of the most human goals.

Further Information:

C Battini and G Landi, ‘3D Tracking Based Augmented Reality for Cultural Heritage Data Management’, Int. Arch. Photogramm. Remote Sens. Spatial Inf. Sci. 40(5). W4. 375-79, 2015.

G Tucci, J L Lerma, Applied Geomatics, Vol 10, Issue 4, 2018.

This article originally appeared as ‘3d digitisation’, in IHBC’s Yearbook 2019, published by The Institute of Historic Building Conservation in 2019. It was written by Alexy Karenowska DPhil, the director of technology at The Institute for Digital Archaeology (http://digitalarchaeology.org.uk/) and a research scientist in Oxford’s Department of Physics where she is a fellow of Magdalen College.

--Institute of Historic Building Conservation