Pompeii, from the excavations in Region IX new light is shed on Roman construction techiniques

New information relating to Roman construction techniques is emerging from the ongoing excavations at the Archaeological Park of Pompeii. In the rooms of the ancient domus in Region IX, insula 10 excavations are revealing important evidence of a building site in full swing: work tools, stacked tiles, bricks of tuff, and piles of lime.

According to scholars, the building site was active up until the day of the eruption of Vesuvius in AD 79, which began around lunchtime and lasted until the morning of the following day. The excavation of this area, aimed at regulating the hydrogeological situation along the boundary between the excavated and unexcavated parts of the Roman city, is revealing the presence of an ancient building site that affected the entire insula block. In particular, abundant evidence of building work in progress can be found in the house with the bakery of Rustius Verus, where a still life depicting a focaccia and a goblet of wine has already been documented in recent months.

The atrium was partially covered, materials for the renovation were piled up on the ground and on the doorjamb to the tablinum (reception room), decorated in the fourth Pompeian style with a mythological painting of 'Achilles at Syrus', one can still read what were probably the tally marks of the building site accounts, i.e. Roman numerals written in charcoal, easily erasable in contrast to the graffiti engraved in the plaster.

Traces of ongoing activities can also be found in the room that housed the lararium (shrine), where amphorae were found that were reused to ‘slake’ the lime used in the plastering process. In several rooms of the house, construction tools were discovered, ranging from lead weights –plumb bobs—for ensuring a perfectly vertical wall ('plumb') to iron hoes used for preparing the mortar and working the lime. Even in the neighbouring house to the east, reached by an internal door, and in a large house to the south, which has so far only been partially investigated, there is a lot of evidence of a large building site, attested by the huge piles of stone rubble to be used in the reconstruction of the walls, as well as broken amphorae, pottery, and tiles kept to be made into cocciopesto (flooring).

This is an 'extraordinary opportunity to experience the potential of close collaboration between archaeologists and scientists of materials,' write the authors of an article published in the E-Journal of the excavations of Pompeii. In the analysis of materials and construction techniques, the Archaeological Park of Pompeii was supported by a team of experts from the Massachusetts Institute of Technology, USA. "The hypothesis put forward by the team is that of hot mixing, i.e. mixing at high temperatures, where quicklime (and not slaked lime) is pre-mixed with dry pozzolana and subsequently hydrated and applied in the construction of the opus caementicium," reads the text.

Normally, quicklime is immersed in water, i.e. 'slaked', long before use on the building site, forming the so-called slaked lime, a material with a plastic consistency. The 'slaking', i.e. the reaction between quicklime and water, produces heat. Only at the time of installation is the lime then mixed with sand and aggregates to produce the mortar or cement.

In the case of the Pompeii building site, on the other hand, it appears that quicklime, i.e. not yet brought into contact with water, was at first only mixed with pozzolanic sand. While the contact with water took place shortly before the wall was laid. This meant that, during the construction of the wall, the mixture of lime, pozzolanic sand and stone was still warm due to the thermal reaction taking place and consequently dried more quickly, shortening the construction time.

In contrast, when it came to plastering the walls, it seems that the lime was first slaked and then mixed with aggregates to be laid, as is still done today.

"Pompeii is a treasure chest and not everything has been revealed in its full beauty. So much material has yet to emerge. In the last Budget Law we financed new excavations throughout Italy, and an important part of this allocation is earmarked precisely for Pompeii,' says the Minister of Culture, Gennaro Sangiuliano. 'I was very pleased when the director of the archaeological park, Gabriel Zuchtriegel, reminded us that never before have so many excavations been active on the site: we can say that this is a record for the last few decades. At the same time, we are also working on other fronts. In recent months, the Minister of Defence, Guido Crosetto, ceded the former Spolettificio di Torre Annunziata to the Ministry of Culture, where a large museum will be built to house all these finds'.

"The excavation in Region IX, insula 10, planned during the years of the Great Pompeii Project is yielding, as was to be expected, important results for furthering our knowledge of the ancient city. An interdisciplinary research site, born from the previous excavation of Region V, from the need to consolidate the limits of the excavations, i.e. the walls of eruptive material left by 19th and 20th century excavations that loom dangerously over the excavated areas. Pompeii continues to be a permanent building site where research, consolidation, maintenance and capacity for development are related activities and daily practice," says the Director General for Museums, Massimo Osanna.

"It is yet another example of how the small city of Pompeii makes us understand so many things about the great Roman Empire, not least the use of cement. Without cement, we would have neither the Colosseum, nor the Pantheon, nor the Baths of Caracalla. The excavations currently underway in Pompeii offer an opportunity to observe almost live how an ancient building site functioned," emphasises Park Director Gabriel Zuchtriegel. The data emerging seems to point to the use of quicklime in the construction phase of the walls, a practice already hypothesised in the past and capable of considerably speeding up the time of a new construction, but also of the renovation of buildings damaged, for example, by an earthquake. This seems to have been a widespread situation in Pompeii, where work was in progress almost everywhere, so it is likely that after the great earthquake of AD 62, seventeen years before the eruption, there were other seismic tremors that struck the city before the cataclysm of AD 79. Now we are forming a network between research institutions to study the building know-how of the ancient Romans: maybe we can learn from them, think about sustainability and reuse of materials”.