Pompeii through the ages

Scientists from Fraunhofer and Max Planck institutes are studying the history of the restoration of Pompeii, which has been a UNESCO world heritage site since 1997, and are developing innovative materials and processes for conserving the city’s ancient sites.

Pia Kastenmeier has known Pompeii for over 20 years now. The archaeologist, who carries out research at the Max Planck Society’s Kunsthistorisches Institut in Florenz, spends most of her time in the ancient city at the foot of Mount Vesuvius in Naples. “It is a huge privilege to work here,” she says.

Over two million people visit the 66-hectare site every year, which has been excavated since 1748. Around one third of the ancient city is still covered in ash and pumice; it was completely buried by a volcanic euruption of Mount Vesuvius in 79 AD.

Johann Wolfgang von Goethe, who visited the excavations on his journey to Italy (1786 - 1788), described how, even then, the walls were being destroyed “little by little”. For this reason, no further buildings and streets have been uncovered in Pompeii since the 1980s, as adverse environmental and weather conditions continue to eat into the walls, frescoes and mosaics. The crowds of tourists also leave their traces.

Together with Katrin Wilhelm, a colleague from the Fraunhofer Institute for Building Physics (IBP), Pia Kastenmeier coordinates the art and cultural science expertise from her own institute and the technological skills provided by the Fraunhofer scientists with a view to understanding how the monuments were handled over the years, and how Pompeii’s cultural heritage can be protected in the long term. “We are working on an interdisciplinary basis. This is innovative, as engineers and humanities scholars rarely get to work jointly on projects like this. The cooperation with the local monuments office, the Parco Archeologico di Pompei, is also very positive. "

Pompeii – irrevocably altered by restoration

What awaits the visitor in Pompeii today is not only a fascinating ancient site but also the juxtaposition and superimposition of many different interpretations and imaginings of an ancient cityscape. Like historical manuscripts that were repeatedly overwritten, there is no longer just one Pompeii today. The city has been transformed repeatedly over the course of time and has many different versions. Even Pia Kastenmeier, who knows Pompeii down to the last detail, was surprised to discover during her archive studies that she barely recognised individual buildings as they had changed so radically over the centuries.

“Every restoration intervention of the last 250 years provides information about the person who commissioned it, the person who carried it out and their ideas about ancient architecture,” explains Gerhard Wolf, Director of the Max Planck Society’s Kunsthistorisches Institut in Florenz and Project Leader. Based on intensive archive and literature research and the consultation of previously unpublished sources, the art historians are carrying out a comprehensive survey of the restoration and history of the museumisation of Pompeii for the first time. As part of this process, they have digitised large volumes of documents. “In addition to the predominantly archaeological literature on Pompeii, a considerable number of publications were produced about the city in which it featured prominently as the icon of a constantly reinvented antiquity. These publications gave Pompeii the mythical aura that surrounds it to the present day,” explains Wolf.

The sources include travelogues and antiquarian literature, drawings and sketches by architects and artists, art history studies and aesthetics treatises on the mosaics and frescoes, and old photographs. This contrasts with the 250-year-long “life” of an archaeological site, whose physical appearance has changed constantly, be it due to natural decay or the efforts to conserve it.

Optimal mortar for use in restoration

The basis for the analysis and dating of historical mortar was established 30 years ago, however the technical possibilities available for such tasks have developed considerably since then.  New, minimally invasive and non-destructive examination methods and computer-assisted analyses of large data volumes have prompted major advances in both the knowledge and technology available in this area.

“However this high-tech research has rarely been used in the area of cultural heritage up to now,” says Ralf Kilian, an engineer and restoration expert from the Fraunhofer IBP.  The new methods have now been transposed, further developed and verified using traditional mortar analysis methods.

“The Romans developed mortar technology to an extremely high level over the centuries,” reports Gerhard Wolf, Director at the Max Planck Society's Kunsthistorisches Institut in Florence, together with Klaus Sedlebauer (Fraunhofer IBP), project leader on the Max Planck side. “The ancient source text, The Ten Books on Architecture by Vitruvius, describes plaster bases with up to seven layers of mortar, all with different characteristics depending on their function.” However such detailed work has only rarely been discovered in Pompeii where two- to three-layer plaster coats are more common. To conserve these ancient surfaces in the long term, optimally adapted restoration mortars are needed whose material properties are tailored to the original mortar.

The building physicists from the IBP analysed the restoration processes used in Pompeii in detail during the first two years of the cooperation programme "Pompeii Arch&Lab"; particular attention was focused on the architectural surfaces and mortars that form the bases for the frescoes. 30 different types of mortars that were used in the period between 1850 and 1970 could be identified.

One of them proved to be particularly durable and succeeded in conserving the architecture and decorations for a long time: a lime mortar that was very common in the nineteenth century was applied carefully in two layers – an underlayer and a thinner upper layer – and mixed with sands and pozzolan. In contrast, the cement mortars that were later used were far too hard and contributed to destroying the plaster on the walls of many buildings. 

“Based on our initial findings we hope to develop individually-tailored mineral and organic binders and aggregates for use in restoration processes that will provide the most long-lasting conservation effects,” explains Kilian.

Pompeii lives on in today's cities

In addition to this restoration project, the art historians are also focusing on the complex process of analysing the museumisation of Pompeii, that is the idea of its ancient lifeworld as formed in the National Archaeological Museum of Naples from the early nineteenth century. Implements, artefacts, statues, vases, frescoes and mosaics were taken to the museum from Pompeii and arranged there in a new architectural context. The image of Pompeii that arose as a result influenced, among other things, post-industrial-revolution European architecture and urban planning. The ceramics, bronzes, sculptures, floor mosaics, frescoes, fountains and villa architecture provided an ideal model. “Even in today’s cities, there is a lot more Pompeii than you’d think,” says Gabriella Cianciolo Cosentino, the project's architectural historian.  

It is planned to present the findings of the four-year cooperation programme in a book to be published around two years from now. In addition to conferences, an exhibition is being planned which should “demonstrate how, why and when Pompeii was restored or reconstructed and the political and ideological motivations behind these measures”.

SB/BA