During the Roman era, the southern promontory of the Gulf of Baia (in Latin Baiae) was the perfect location for constructing villae maritimae for the Roman elite, who chose to spend their summer residences by the sea, while also cultivating fish and oysters.

One of these residences is located today in the military fortress of the Castello Aragonese di Baia, built in 1495 AD during the Aragonese period. Here, during restoration works, archaeologists unearthed the ruins of the residential sector of the villa, which historical sources attribute to Julius Caesar. The most representative proof of this, archaeologists said, are the exceptional in situ remains of mosaics, decorated plasters, and finely painted fresco surfaces, decorated in the repertoire of the Second Style.

Among the most impressive finds is a monumental fresco adorning a wall in opus quasi reticulatum, a construction technique typical of the late Republican period. This fresco, dated by experts between 60 and 50 BC, depicts an architectural scene in perspective using trompe l’oeil, an illusionistic style that creates the impression of depth and three-dimensionality on a flat surface.

3D recontruction of wall in opus quasi reticulatum preserving, in its upper part, the perspective depiction of architectural scenes en trompe l'oeil, decorated according the II style repertoire, and details of the areas where non-invasive analyses have been performed
3D recontruction of wall in opus quasi reticulatum preserving, in its upper part, the perspective depiction of architectural scenes en trompe l’oeil, decorated according the II style repertoire, and details of the areas where non-invasive analyses have been performed. Credit: P. Cappelletti et al.

The central composition features a round arch framed by intense red drapery, revealing a tholos, a circular temple supported by twelve majestic columns. In the foreground, a portico with Ionic columns adds depth to the scene, while the background is tinted with green hues evoking an ethereal sky.

What has especially intrigued researchers is the detailed analysis of the pigments used in these wall paintings. Using a battery of cutting-edge, non-invasive techniques, including Raman spectroscopy, portable X-ray fluorescence, and Fourier transform infrared spectroscopy, scientists have identified a palette of colors that is not only diverse but also incredibly expensive by the standards of the time.

The most surprising discovery has been the widespread presence of cinnabar, a bright red pigment composed of mercury sulfide, known in antiquity for being more valuable than gold. This pigment, used extensively in the red draperies and in the monochromatic backgrounds of the lateral decorations, is a testament to the power and wealth of the villa’s owner.

Images of each colour hue acquired in situ on the frescoed surfaces via digital microscopy.
Images of each colour hue acquired in situ on the frescoed surfaces via digital microscopy. Credit: P. Cappelletti et al.

The legal price for pigments set cinnabar at 70 sesterces per pound, compared to 6 denarii for minium or 2 denarii for hematite, the researchers note. This is why painters often mixed cinnabar with less expensive pigments like red ochre.

In addition to cinnabar, other precious pigments have been identified, such as Egyptian blue, red and yellow ochres, and copper-based green compounds, all applied on a fresh lime substrate, following the true fresco technique that ensured the durability of the paintings.

The technical sophistication of these wall decorations goes beyond the choice of pigments. Analyses have revealed a masterful use of color mixing to create shading and volume effects, as seen in the white columns subtly painted with iron-based pigments to simulate relief. Likewise, the presence of organic pigments in the pink areas suggests a level of artistic refinement reserved only for the most prestigious residences.

Thermogram and optical images of the rear fresco
Thermogram and optical images of the rear fresco. Credit: P. Cappelletti et al.

Researchers have also detected the presence of synthetic resins, likely applied in modern attempts to preserve the paintings, as well as degradation products such as gypsum, indicating the ongoing challenges in conserving these archaeological treasures.

The opulence of the decoration and the choice of iconographic themes reflect not only the personal taste of the owner but also the aspirations and values of a ruling class on the eve of profound social and political changes.

The mural decoration of this villa, unlike the more famous frescoes in the Vesuvian area, is one of the very few testimonies of late Republican decorative apparatus present in the Phlegraean Fields, due to the transformation of the landscape, the historical stratification of the sites, bradyseism, and, unfortunately, unauthorized construction activities, the researchers say.

SOURCES

Cappelletti, P., De Bonis, A., Di Martire, D. et al. The Roman villa at the Castle of Baia (Naples, Italy): investigations on the polychromy of frescoed surfaces by using non-destructive spectroscopic techniques. Herit Sci 12, 328 (2024). doi.org/10.1186/s40494-024-01436-6

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