Researchers in the University of Oxford's Department of Chemistry have solved a decades-old archaeological puzzle by re-investigating the molecular composition of an intriguing residue found in bronze jars excavated from a 6th century BCE Greek shrine in Paestum, southern Italy. Published today in the Journal of the American Chemical Society , the study presents the first biomolecular evidence that the residue once contained honey, likely in the form of honeycomb.
This research is a reminder that archaeological collections hold untapped scientific potential and how new information can be revealed when modern analytical techniques and multidisciplinary collaborations are combined.
Project co-lead Dr Luciana da Costa Carvalho, Department of Chemistry
The underground shrine, about an hour and a half's drive away from Pompeii, was originally discovered in 1954 and included several bronze jars containing an orange-brown sticky substance. At the time, archaeologists assumed the residue was honey, since this was an important substance in the ancient world, often left in shrines as offerings to the gods or buried alongside the dead. However, over the course of 30 years, three different teams analysed the residue but failed to confirm the presence of honey. Instead, they concluded that the jars contained some sort of animal or vegetable fat contaminated with pollen and insect parts.
In this new study, the researchers used a suite of modern analytical techniques, including mass spectrometry for proteins and small molecule compositional analysis, to determine its molecular makeup. This integrated approach enabled the identification of sugars, organic acids, and royal jelly proteins that would have remained undetected using a single method. The results demonstrated that the ancient residue had a near-identical chemical fingerprint to modern beeswax and similar to modern honey.
Further insights came from comparing the results obtained for the residue with the results from analyses of modern honeycomb samples, and experimental simulations of degraded honeycomb.
Professor James McCullagh , Director of Oxford's Mass Spectrometry Research Facility in the Department of Chemistry who co-led the project, said: 'The application of multiple analytical techniques was key to the success of this study. By applying several mass spectrometry and spectroscopic approaches we were able to reveal a comprehensive picture of the residue's molecular composition - enabling us to distinguish between contaminants, degradation products, and original biomarkers.'
Dr Luciana Carvalho using a thermal separation probe. Image credit: Thomas Player.'We used X-ray photoelectron spectroscopy to analyse the surface of the residue and found copper corrosion products closely associated with it,' added lead author Dr Luciana da Costa Carvalho, a postdoctoral researcher in the Department of Chemistry. 'Copper ions are naturally biocidal, and we believe their presence may have helped protect the sugar markers in this area from microbial decay.'
The study was made possible due to a close partnership between the University of Oxford's Ashmolean Museum and the Archaeological Park of Pompeii. Dr Kelly Domoney , Heritage Science Manager at the Ashmolean Museum who co-led the study, explained: 'In preparation for the exhibition "Last Supper in Pompeii" at the Ashmolean Museum in 2019, our colleagues at the Archaeological Park of Paestum and Veila generously made several important and high-profile loans, including a Greek bronze hydria from the Heroon and its organic contents. We were permitted a unique opportunity to re-analyse those contents using modern instrumentation at the University.'
Dr Luciana da Costa Carvalho describes the results of the study.
For the exhibition, 37 objects were carefully assessed, with techniques that included microscopy and X-radiography, to inform their future conservation. In many cases, this revealed new information about how the objects were made and used. For instance, some vessels retained soot from cooking hearths on the underside of the base, whilst others showed thick accumulation of limescale on the interior, demonstrating that they were used as kettles for heating water.
The turning point in the project came with the identification of major royal jelly proteins all specific to honeybee secretions. Our results demonstrate the power of bottom-up proteomics combined with metabolomics in the investigation of archaeological samples.
Co-author Elisabete Pires , Department of Chemistry
Co-author Dr Gabriel Zuchtriegel, Director of the Archaeological Park of Pompeii and former Director of the Archaeological Park of Paestum & Velia, said: 'The application of chemical and scientific analyses to extract new and detailed information from existing artefacts allows us to adopt a more informed and nuanced approach to understanding the lives and rituals of past societies, and all from material that already lines the shelves of every archaeological museum collection.'
The authors hope this work will inspire further re-analysis of legacy materials, especially those held in museum collections where sampling is limited and earlier tests proved inconclusive.
The study 'A Symbol of Immortality: Evidence of Honey in Bronze Jars Found in a Paestum Shrine Dating to 530-510 BCE' has been published in the Journal of the American Chemical Society .
