Echoing forever: 2,100-year-old Alexander the Great mosaic analyzed for restoration

Example of estimation of external treatment placement by multispectral imaging and interpolation of multi-technique studies. Credit: PLOS ONE (2025). DOI: 10.1371/journal.pone.0315188
In 333 BC, a fierce battle took place between the armies of Alexander the Great and the Persian king Darius III near the small Pinarus River along the border between present-day Turkey and Syria. Here, at the Battle of Issus, Alexander’s army of 75,000 Greeks faced Darius’ vastly superior force of approximately 600,000 Persians.
The army numbers in these ancient written sources are probably greatly exaggerated, as modern accounts of the battle put them much lower, but for the better part of 2,300 years this story was told. It’s been a long time since I’ve been in the middle of a long time.
This victory was a pivotal accomplishment in Alexander’s campaign and cemented his reputation as one of the greatest military commanders in history. Some 200 years after the Battle of Issus, the Alexander Mosaic was created on the floor of the Faun’s House in Pompeii, either as a glorification and commemoration of the historical event, or simply as an adaptation of Greek art to the Roman style. Elite decoration. It is currently housed at the National Archaeological Museum (MANN) in Naples, Italy.
Probably a Roman copy of an early (c. 300 BC) Hellenistic painting by Philoxenus of Eretria, this mosaic depicts scenes of confusion, terror, and triumph. It depicts the climactic moment when Alexander leads the final charge. Alexander pierces the Persian defenders with his spear and looks upon Darius III in despair. The driver orders the horses to retreat completely.


Field analysis with Alexander Mosaic (MANN, Naples, Italy). Credit: PLOS ONE (2025). DOI: 10.1371/journal.pone.0315188
Measuring 5.82 x 3.13 meters and consisting of more than 1.9 million individual tiles smaller than 4 mm, the mosaic was constructed using opus vermiculatum technology to create a highly detailed representation. Considering its intricate craftsmanship, ancient age and need for conservation, researchers from the University of Naples Federico II, in collaboration with MANN, adopted non-invasive techniques to investigate the mosaic .
In a study published in PLOS ONE, “From Tiny to Giant: A Geological Spotlight on the Alexander Mosaic (National Archaeological Museum of Naples, Italy) Using Non-Invasive In-Situ Analysis,” researchers assessed the condition of the mosaic. We used non-destructive analytical techniques to Investigate methods of preservation, examine its construction materials, and hypothesize about the geological origin of the tiles. The findings detail the mosaic’s complex composition and susceptibility to deterioration, as well as provide evidence-based data for restoration.
Multispectral imaging illuminated the artwork by capturing reflectance and luminescence images across 64 areas, revealing the tiles’ complex colors, signs of surface deterioration, and evidence of past treatments. Portable X-ray fluorescence analysis provided a detailed look at the chemistry of the mosaic, with 144 precise point analyzes mapping the elemental composition of the tiles.
Fourier transform infrared spectroscopy and Raman spectroscopy were used to understand the mineral content to identify the materials used. Infrared thermography provided a thermal perspective and scanned six major sections to detect temperature anomalies indicative of underlying conservation challenges.


Representative OM images of colored tesserae. Credit: PLOS ONE (2025). DOI: 10.1371/journal.pone.0315188
The light microscope zoomed in further to capture detailed images of the tiles and the mortar that holds them together. Finally, endoscopy allowed researchers to go behind the surface of the mosaic, revealing structural features and materials introduced during past restoration efforts.
Traces of gypsum, wax coating, and calcium oxalate were visible on the surface. The wax was likely applied during restoration in the 19th century, and the plaster may have been transferred from a protective layer used during transport during the 1843 transfer to MANN. Multispectral imaging highlighted additional surface materials including organic coatings, while infrared thermography detected thermally unstable regions unrelated to previously treated parts.
The tiles were grouped into four categories based on different configurations chosen for each color. The carbonate-based tiles (white, pink, red, yellow, green, and light blue) are likely sourced from Italian and Mediterranean marbles such as Marmor lunensis and Marmor numidicum.
Silicate-based (black, gray, green) tiles can be derived from volcanic or metamorphic rocks. Intermediate/vitreous materials (yellow, green, brown, red). Some contain glass components. The black and red tiles, which contain high concentrations of Fe and Mn, may have been sourced from Roman black stones like Nero Antico.
Endoscopy of the back surface revealed voids and evidence of past adhesive applications. Thermal images showed deformation and mortar instability, giving conservators the insight needed to successfully implement structural reinforcement in future restoration efforts. Additional analyzes of mortar samples and images are planned to complement these findings.
Further information: Giuseppina Balassone et al., “From the small to the gigantic: a geological spotlight on the Alexander Mosaic (National Archaeological Museum of Naples, Italy) using non-invasive in-situ analysis”, PLOS ONE (2025). DOI: 10.1371/journal.pone.0315188
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Citation: Echoing Eternity: 2,100-year-old Alexander the Great Mosaic Analyzed for Restoration (January 18, 2025) https://phys.org/news/2025-01-echoing-eternity-year-alexander Retrieved January 18, 2025 from-great.html
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