The Alexander Mosaic, housed in the National Archaeological Museum of Naples (MANN), is one of the most significant works of Roman antiquity. This mosaic, with monumental dimensions (583 x 325 cm) and composed of approximately 1.9 million tesserae, depicts the Battle of Issus, where Alexander the Great led the Macedonians to victory against the Persian army of Darius III.

Since its discovery in Pompeii in 1831, this piece has captivated artistic fascination and, more recently, been the subject of non-invasive scientific investigations aimed at preserving its historical integrity.

The artwork was found in the House of the Faun, one of the most luxurious residences in Pompeii, buried by the eruption of Mount Vesuvius in 79 AD. Its technique, known as opus vermiculatum, allows for exceptional pictorial detail through tiny tesserae that masterfully recreate Alexander’s face and the battle scenes. According to experts, this mosaic is a copy of a lost Hellenistic painting, probably by Philoxenus of Eretria, dated around 315 BC.

Napoli Mosaic Issos Alexander
The Alexander Mosaic and some pictures displaying the nondestructive noninvasive archaeometric campaign. Credit: G. Balassone et al.

In 2020, the MANN launched an ambitious project to restore the mosaic, supported by non-destructive analysis methods that combine advanced technology with interdisciplinary techniques. Tools such as digital video microscopy, Raman spectroscopy, infrared thermography, and portable X-ray fluorescence analysis were employed, among others.

These techniques allowed researchers to map the chemical and mineralogical composition of the tesserae, identify ancient conservation materials, and assess the mosaic’s structural condition.

One of the most significant discoveries was the identification of ten distinct colors in the tesserae, crafted from natural materials such as carbonates, silicates, and colored glass. Additionally, traces of materials used in past restorations, such as plaster and natural waxes, were found, which had been applied to consolidate the artwork in the 19th century. While these substances aimed to protect the surface, they also contributed to the mosaic’s deterioration due to humidity and chemical reactions over time.

Napoli Mosaic Issos Alexander
The different types and colors of tesserae found in the mosaic. Credit: G. Balassone et al.

The conservation of the mosaic faces significant challenges, such as deformations in the tesserae caused by mechanical stress and fluctuations in temperature and humidity. Infrared thermography identified areas with thermal anomalies, indicating potential structural vulnerabilities. Moreover, multispectral imaging revealed the presence of protective materials applied during its relocation to the museum in the 19th century, many of which need to be removed or stabilized.

Archaeometric analysis enabled researchers to propose possible geological sources for the tesserae, located in Mediterranean regions such as Italy, Greece, the Iberian Peninsula, and Tunisia. For instance, the white tesserae might derive from Carrara marble, while the green and black ones could originate from serpentinites and basalts either locally sourced or from other parts of the Roman Empire.

The mosaic remains the subject of ongoing research, with new data obtained through endoscopies of its reverse side and three-dimensional analyses of its internal structure. This comprehensive approach not only ensures its proper restoration but also contributes to advancing knowledge about artistic techniques and materials of antiquity.


SOURCES

Balassone G, Cappelletti P, De Bonis A, De Simone A, Di Martire D, Graziano SF, et al. (2025) From tiny to immense: Geological spotlight on the Alexander Mosaic (National Archaeological Museum of Naples, Italy) using non-invasive in situ analyses. PLoS ONE 20(1): e0315188. doi.org/10.1371/journal.pone.0315188


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