## 5 Results and Discussion  
### Archaeometric and Diagnostic Analysis  
Petrographic analysis by POM was carried out to define the textural and compositional characteristics of all examined samples. Descriptions were made by grouping the samples (i.e., 10 groups) depending on the stone material type. Some representative photomicrographs are shown in Figure 4, while Table 3 synthesizes the main features of each sample. Regarding the mosaic's _tesserae_, analyses permitted to characterize materials considering their originality within the mosaic, since some sampled _tesserae_ are attributable to previous restoration intervention. Figure 4: Microphotograph (by polarized optical microscopy (POM), in parallel (PPL) and crossed (CPL) polarized light) showing textural features of some selected brick, mortar, metamorphic, sedimentary and volcanic rock fragments, according to the 10 groups, with some evidence of the degradation layer on the surface. TTB6 (I group); TTBi1 (II group); TTN1 (III group); TTN1 (IV group); TTGi1 (V group); TTR1 (VI group); TTRi1 (VII group); TLM1 (VIII group); TL1 (IX group) and TC1 (X group). The red dotted line in TTB6, TTBi1, TTR1 demarcates the layer of the alteration patina from the substrate. The white dotted line in TTB6 demarcates the layer of the residues of bedding mortar from the substrate. I group  
On the basis of textural features, samples belonging to the first group, which includes original white mosaic's _lesserae_ (i.e., samples TTB1, TTB2, TTB3, TTB4, TTB5 and TTB6) can be classified such as biomicrites, according to [PERSON] (1959) [38], or wackestones, according to [PERSON] (1962) [39]. They show a mud-supported texture (which contains more than 10% grains), where the allochemical component is mainly made up of bioclasts (25-30%) (mostly microforaminifera). Dissolution phenomena and recrystallization of secondary calcite occur in some fragments. Overall, tiles are compact, poorly degraded, with both primary and secondary porosity not exceeding 3%. Residues of the bedding mortar, mostly made up of quartz crystals with sub-angular to sub-rounded shapes, along with plagioclase and mica are also visible. Finally, regarding their state of conservation, samples show a thin and brownish superficial alteration layer with an average thickness of about 200 \(\upmu\)m (Figure 4). II group  
The second group includes the samples TTB11, TTB11 and TTB2, which are part of the replacement white mosaic's _lesserae_. As for TTB11, the fragment can be classified such as biomicrite, according to [PERSON] (1959) [38], or wackestone, according to [PERSON] (1962) [39] where fossilized planktonic foraminifera (i.e., globigerinae and globotruncanae) and bioclasts represent the dominant allochemical components. Precipitation of secondary calcite within in bioclasts is also visible. The sample appears devoid of fractures and the porosity does not exceed 3%. Additionally, TTB11 displays a thin and brownish superficial alteration layer with an average thickness of up to 100 \(\upmu\)m. Regarding TTB11 and TTB12, both _tesserae_ are carbonic rocks with a grain-supported fabric, interstitial matrix and the presence of intraclasts, classifiable as packstones according to [PERSON] classification (1962) [39] and intrasparites according to the [PERSON] one (1959) [38]. Samples show a relatively altered matrix characterized by highly altered plagioclase and quartz crystals. Recrystallization phenomena of secondary calcite grains in areas subject to dissolution are also common. III group  
The third group includes four original black mosaic's _tesserae_ (i.e., samples TTN1, TTN2, TTN3 and TTN4). These samples can be classified such as effusive igneous rocks with a porphyritic structure and a fine-grained groundmass ranging from crypto to microcrystalline. As phenocrysts, feldspars and plagioclase were mostly recognized, followed by pyroxenes and opaque mineral oxides. Overall, these _tesserae_ are in a good state of preservation. No superficial alteration layers and patinas were detected.