## 2 Archaeological and Geological Context  
The ancient city of _Halaesa Archonidea_ is located on the eastern slope of a hill overlooking the Tyrrhenian Sea (see Figure 1), along the lower valley of the Tusa stream, known in antiquity as the _Halaisos_ River.  
According to ancient sources, the city was founded in 403 BC by _[PERSON]_, lord of _Herbita_, on a hill approximately 8 stadia (about 1500 m) from the sea [34]. During the Hellenistic-Roman period, _Halaesa_ was renowned for its great economic prosperity, largely driven by maritime trade. However, it was particularly notable for its privileged relationship with Rome [35]. Along with four other cities in Sicily, it was granted significant privileges, including tax immunity. [PERSON] even listed _Halaesa_ among the _civitates immunes ac libreae_[36], cities that enjoyed both tax exemption and self-governance. In the Augustan era, _Halaesa_ attained the status of _municiipum_, and throughout the imperial age, it remained one of the most significant cities on Sicily's northern coast. It was regarded as the principal port where agricultural products from the island's interior were gathered before being shipped to Rome [35].  
Most of the buildings in the city, many of which remain partially visible, were constructed during the Hellenistic-Roman period, a time of significant architectural development. For their construction, the inhabitants primarily used locally sourced materials, e.g., argillite, ensuring both availability and practicality.  
To date, archaeological investigations of the Sanctuary of Apollo have focused solely on its accessible areas, as the western half remains on private property. Despite this limitation, excavations have revealed a large square, with a rectangular platform over 40 m long in the northern half. On top of this platform stood three Roman-Italic-type temples, all facing east. Only the massive foundations of these temples, built from squared blocks of local argillite, remain in situ (Figure 2).  
Figure 1: Geolocation map of the archaeological site of _Halaesa_ (Sicily, Italy), with a drone view of the ancient city of _Halaesa Archonidea_ (from the north).  
Figure 2: (**a**) Aerial and (**b**) eastern views of a rectangular platform over 40 m long in the northern half of the archaeological site of _Halaesa_ (Sicily, Italy).  
In the largest central temple, remnants of the _cella_ floor, made of white _tesserae_, are still visible [4,37]. The platform's perimeter walls were constructed using a mixed technique, combining argillite and sandstone blocks. These walls cover a natural argillite outcrop, still visible in some areas, which was probably leveled in antiquity to create a more regular platform shape. The same rock outcrop was also encountered in recent excavations south of the square, conducted between 2023 and 2024. These excavations have uncovered the southern boundary of the terrace, marked by a wall made entirely of argillite blocks, along with a structure made using a mixed technique, identified as a monumental stepped altar [38].  
From a geological point of view, the investigated archaeological area falls into the Nebrodi Mountains, which are geologically part of the Apennine-Maghrebian Chain, one of the three main orogenic domains in the central Mediterranean [39]. The hill has a maximum height of 250 m and is located on the hydrographic left of the Tusa stream. In particular, the outcrop area falls within the varied formation called \"Tusa Tufites\" [40], which constitute an arenaceous pelite unit with a variable sandstone/pelite ratio (see Figure 3).  
The lithofacies present in the area are made up of an alternation of micaceous arenites and grey-green tuffites, generally poorly cemented, in layers of 15-40 cm up to banks of 1-2 m, with thin clayey-silsomarly interlayers and, subordinately, whitish marly limestones with conchoidal fractures and medium coarse-grained calcarenites in thin layers [41].