Bridges are infrastructures of primary importance in the history of humanity because they connect the peoples on Earth, facilitating communication between them and allowing the exchange of civilizations and cultures. Bridges are essential for ancient and modern cities and for the road network, to overcome rivers and smaller waterways. They were built in Roman times by valid designers and civilian and military workers, often in conditions of difficult logistic and complex morphological situations, by boats and ships, wood, masonry, and mixed type of materials with masonry substructure and wooden superstructure.

Initially, the task of building roads and bridges was entrusted to magistrates such as the censors, deprived of imperium, tribunes of the plebs, aedili, legacies of the proconsuls. Subsequently, the impressive construction of roads and bridges in the II and I centuries BC created a complex and expensive network of urban and territorial infrastructures because they required, in addition to construction, restoration, reconstruction and maintenance. The road network was attributed to a particular and extraordinary magistrate: the Curator viarum, the governance between the praetorship and the consulate. According to Tito Livio from the II century BC the contract institute was applied (locatio conductio operis) to organize the works for the roads and bridges to tenant entrepreneurs (conductores viarum).

The Roman roads were classified according to their importance, as reported by the surveyor Siculus Flaccus (Adams, 2011).

➢ Public roads were built at the expense of the State and with the name of the builder.

➢ Strategic roads were built by the army at its expense.

➢ Secondary roads were built by villages (pagi).

➢ Private roads were built by land and house owners.

Different bridges were needed for the construction of the old Appian Way, a public road also known as Regina viarum, whose construction began in 312 BC at the request of the censor Appio Claudio Cieco to connect Rome to the port of Brindisi on the Adriatic Sea in Puglia. The enormous importance of this consular road on the connective, commercial and military lines was underlined by Pisani Sartorio (2003), while Chiocchini et al. (2016) faced a little known aspect of Regina viarum, contributing to the identification of its layout between Mirabella Eclano (heir of the ancient Aeclanum, in the middle valley of the Calore River in Campania) and Venosa (Venusia, Latin colony founded in 291 BC in Basilicata) located in the Campania and Basilicata Apennine (Figure 1).

The bridge over the Ofanto River (Flumen Aufidus), also reported in the Tabula Peutingeriana as Pons Aufidi, is a crucial issue in determining where the layout of the old Appian Way between Mirabella Eclano and Venosa had to cross this river in the area between Conza della Campania (heir of the ancient Compsa) and the Santa Venere bridge (SVB) (Figure 2). It should be noted that near Conza della Campania there was another Roman bridge over the Ofanto

River, of which only one pier survived, at present submerged in the basin created by the Conza della Campania dam (Aveta et al., 2012; Chiocchini et al., 2016).

Two hypotheses have been proposed for the layout of the old Appian Way between Mirabella Eclano and Venosa: 1) the nortnern layouts (9, 10, 11, 12, 13 in Figure 2), which crossed the Ofanto River by the SVB, even if this bridge is not really of Roman age, as specified later (Pratilli, 1745; Mommsen, 1848; Jannacchini, 1889; Grasso, 1893; Guarini, 1909; Ashby, 1916-1917; Iacobone, 1935; Lugli, 1952, 1963; Castagnoli, 1969; Alvisi, 1970; Radke, 1981; Stazio, 1987; Quilici, 1989, 2004; Flammia, 1995; Romito, 1995; Johannowsky, 1996; Tazzi, 1998; Fornaro, 2000; Della Portella, 2003; De Luca, 2003; Morano, 2003; Cera, 2011; Ceraudo, 2011; Castrianni, 2013; Del Lungo, 2013; Lariccia, 2015; Marchi & Ferlazzo, 2015; Ceraudo, 2019); 2) the southern layout (14 in Figure 2), which crossed the Ofanto River by the Pietra dell’Oglio bridge (POB) (Mannert, 1823; Lenormant, 1883; De Lorenzo, 1906; Buglione, 1929; Grassi, 2013). This latter hypothesis has been deepened, updated, and documented by Chiocchini et al. (2016) with new widely evident data that demonstrate how this layout is the shortest and most convenient in terms of design and construction, and therefore the most reliable alternative. The hypothesis of the southern layout with the POB was also adopted by Vistoli (2019), while according to Marchi (2019a, 2019b), who deals with the layout of the old Appian Way in Basilicata mentioning the specific arguments of Chiocchini et al. (2016), it is doubtful whether the Pons Aufidi is the SVB or the POB.

As for the POB, it should be noted that there is no specific study aimed at describing its current state, original architectural and structural elements and the materials used for the construction, but only scarce, short and inaccurate information is available on this bridge. In fact, De Lorenzo (1906) and the Gardner Collection (Castrianni, 2013) show two fairly clear photos of the bridge, taken from the left bank of Ofanto River, respectively NW down-stream and NW up-stream. Guarini (1909) and Iacobone (1935) propose two small and unclear photos of the Pietra dell’Olio bridge (later changed to Oglio) seen from NE (down-stream). Buglione (1929) shows a partially unclear photo of the bridge that does not allow to establish the point where it was taken. Gazzola (1963) indicates that the bridge is divided into six large arches and only the two external ones and the piers date back to the Roman age. Unfortunately, there is no evidence of the existence of structures of the Roman age, and in the very small picture, the bridge cannot be seen clearly and neither how it is oriented. O’Connor (1993) incorporates the data of Gazzola (1963). Aveta et al. (2012), who studied the historical bridges of Campania with reference to 26 Roman bridges, among which 4 located in the province of Avellino (Santo Spirito bridge in Casalbore, Pietra dell’Oglio bridge, Annibale’s bridge in San Mango sul Calore, Conza della Campania bridge), describe the POB consisting of four asymmetric arches, of which the first and third are semicircular, while the intermediate one is a reconstructed lowered arch. Furthermore, the fourth arch “had previously been covered for the reconstruction of the road to Monteverde, today visible with difficulty”. However, this arch does not exist, as specified later. Very short references to the bridge are described by Troncone (2013), who indicates the presence of four round arches, and by Carluccio (2013), according to which the bridge is built by the opus incertum technique. Vistoli (2019), in the context of two itinerary stations of the old Appian Way between Aeclanum and Venusia, also provides the description of the POB which, however, is incomplete and insufficient as regards the geomorphological characteristics of the site, the structural and architectonic elements and the type of materials used for the construction of the bridge, in particular the quality of the recent mortar and the dated one. Marchi (2019a, 2019b) refers to the data of the POB according to Vistoli (2019).

The research is framed in the activity carried out by the Associazione Nazionale per gli Interessi del Mezzogiorno d’Italia (ANIMI)—Società Magna Grecia in relation to the interdisciplinary work focused on the study of archaeological sites and their environmental context, and the techniques of Geoarchaeology (Rapp & Hill, 1998; Pollard, 1999; Ghilardi & Desruelles, 2009; Shahack-Gross, 2017; Gilbert, 2017; Gençer & Turan, 2017; Leonardi, 2017; Cortéz Pérez et al., 2018; Shillito et al., 2019) have been applied in order to: 1) illustrate the geological and geomorphological setting of the POB area; 2) describe the current state of the POB, its original architectural and structural elements, and their raw materials, to identify the possible construction period; 3) establish whether the POB is the Pons Aufidi of the old Appian Way; 4) improve the knowledge on the construction techniques of Roman bridges, particularly in Campania.

The POB, located in the extreme southeastern sector of the municipality of Aquilonia (province of Avellino, Campania) close to the border with Basilicata in Section IV NO of Sheet 187 Melfi at scale 1:25,000 (coordinates of southeastern entrance of the bridge: 40˚57'54" latitude N and 15˚33'50" longitude E), was used initially to connect Monteverde to its railway station, successively also to the national road SS 401 dir. The bridge crosses, with a NW-SE orientation, perpendicularly the Ofanto River (281 m asl), flowing from SW to NE, at the height of the Mt. Teuto (598 m asl)—Bosco di Pietra Palomba ridge (514 - 318 m asl) and Foggiano (424 m asl) (Figure 2 and Figure 3).

The bridge study operations were developed in four phases. The first phase was dedicated to the acquisition of historical data from the Municipality of Aquilonia, the Engineer of Avellino and the State Archive of Napoli.

The second phase included the following activities. 1) The definition of the geological and geomorphological setting of the POB by the field checking of the survey by Centamore et al. (1971) and updating it to the Sheet 451 Melfi of the Italian Geological Mapat scale 1:50,000 (Istituto Superiore per la Protezione e la

Ricerca Ambientale—Servizio Geologico d’Italia, in print-a). The color of the rocks was defined by the Rock—Color Chart (Geological Society of America, 1991). 2) The execution of a) the partial cut of the weed and climbing vegetation that covers many bridge structures; b) a first material survey by the Professional BOSCH GLM 250 VF Laser Digital Distance Detector to define the current state of the architectural and structural elements of the bridge; c) a second material survey by a Laser Scanner Focus^3D S to check in detail the dimensions of these elements, and d) the aerial video shooting using the aircraft with remote controlled pilot (drone models DJI Phantom 4 and Phantom 4 PRO). 3) The analysis of the masonry textures of the original architectural and structural elements and their construction techniques. 4) The acquisition of 15 samples of the materials used to build the bridge, 10 of which from the outcrops (alluvial pebbles, phytoclastic travertine, sandstone, which was extracted by the HILTI electric core drilling machine), 2 phytoclastic travertine samples from two arches of the bridge and 3 samples of mortar from the latter and from a pier.

The following investigations were carried out in the third phase. 1) An electrical resistivity tomography to define the thickness of alluvial deposits and the underlying substrate, performed by the geo-resistivity-meter M.A.E. A6000SE, producing the energization by means of electrodes driven into the ground with unit spacing of 2 m and simultaneously acquiring the apparent resistivity (pa) and soil chargeability (I.P.). The data recording was carried out according to the Dipole-Dipole-Axial scheme, which allows to better read the lateral discontinuities, and for the data processing the Res2Dinvi software was used. 2) A detailed inspection was carried out in the SVB area, located about 15 km north of the POB, to verify the presence of remains attributable to a Roman age bridge.

The fourth phase was dedicated to the following laboratory analyses and tests (Marra et al., 2015; Columbu et al., 2018; Sitzia, et al., 2020). 1) The mineralogical analysis of the mortar by the X-ray powder diffractometer Siemens D5000 with Gragg-Brentano and radiation λ_KαCu geometry, in which the crystalline powder under examination is placed on a flat sample holder with a scan range of 2.5˚ < 2θ < 140˚. 2) The investigation of the samples of stone materials and mortar by the polarized microscope Zeiss Axioskop on 30 µm thin sections. The modal analysis of the mortar samples by point counter on 300 points for each thin section. 3) The recognition of particular forms of calcite in the mortar by the FEI Quanta-400 Scanning Electron Microscopy (SEM). 4) The tests to determine the dry masses (m_d) at 105˚C ± 5˚C of the cubic samples (10 × 10 × 10 mm) of mortar were carried out by the analytical balance Sartorius Entris153-1s. The real volume (V_r) and bulk volume (V_b) were determined by the Regnault pycnometer for solids with cap 100 ml. The bulk volume (V_b) was calculated as:

V b = [ ( m w − m h ) / ρ w 25 ˚ C ] × 100 (1)

where m_w is the wet mass, m_h is the hydrostatic mass of the wet sample, and ρ_w25˚C is the density of the water (0.9970 g/cm³) at temperature of 25˚C. The apparent density (ρ_b) and the real density (ρ_r) were computed as:

ρ b = m d / V b ;   ρ r = m d / V r . (2)

5) The preparation of four cores of ACP Sandstone for its mechanical characterization according to the recommendations of ASTM (2014) and I.S.R.M. (1994): verification of the perpendicular position of the base faces of cores with respect to their axis; checking of the lateral surface of the cores which must be smooth; measurement of the length and diameter of the cores as the average of two diameters orthogonal to each other. 6) The execution of two uniaxial compression tests and two tensile tests on the four cores by a Controls brand press with controlled load.

As for the construction of Roman bridges, we refer to the monumental works of O’Connor (1993) and Galliazzo (1995), which are still up today the most comprehensive, in-depth, and detailed ones (Cortéz Pérez et al., 2018; Inglese & Paris, 2020). In fact, these two Authors describe the historical, architectural, structural, archaeological, typological, and planning aspects (from the works of foundation to the walking floor, the furnishings, the defenses) and methodology on the possibility of dating, respectively, about 330 and 1560 bridges in different areas of Europe and the Middle East. As for the architectural elements, reference is made to the equally monumental work of Lugli (1957), still considered one of the most complete and precise studies on this topic (Adams, 2011; Aveta et al., 2012; Inglese & Paris, 2020). Finally, the study by Aveta et al. (2012) provided valuable support for the conservation status and construction techniques of the historic bridges in Campania.

The study area is located in the middle valley of the Ofanto River hosted in a tectonic depression oriented west-east inside the Campania and Basilicata Apennine, mainly consisting of clays, sands and conglomerates of the Pliocene Ruvo del Monte Synthem, and subordinately of Mesozoic-Cenozoic formations (Figure 1 and Figure 2) (Sheet 450 S. Angelo dei Lombardi and Sheet 451 Melfi of the Geological Mapof Italy at scale 1:50,000) (Istituto Superiore per la Protezione e la Ricerca Ambientale—Servizio Geologico d’Italia, in print-a, in print-b). This area is in contact with the western edge of the Mt. Vulture’s volcanic complex (Figure 2) with geochemical characteristics similar to those of the Campania Province (affinity with potassium and ultra-potassium series), active with pyroclastic deposits and lava flows during middle Pleistocene between 0.740 and 0.140 Ma (Sheet 450 S. Angelo dei Lombardi and Sheet 451 Melfi of the Geological Mapof Italy at scale 1:50,000) (Istituto Superiore per la Protezione e la Ricerca Ambientale—Servizio Geologico d’Italia, in print-a, in print-b). Figure 3 shows the geological map of the bridge area in the section IV NO of the Sheet 187 Melfi at scale 1:25,000 of the Military Geographic Institute, and Figure 4 the corresponding geological section. The stratigraphic succession includes the following formations (Figure 3): the Cretaceous-lower Miocene Varicolored Clays Formation (red, green, gray clays, marls, marly and siliceous limestones, turbidite calcarenites with chaotic structure; AVR); the lower Miocene calcareous member of the AVR (turbidite calcarenites and marls; AVR₁); the lower Miocene Numidian Flysch (well cemented turbidite medium-coarse quartz-arenites of dark yellow orange color 10 YR 6/6 with thick and very thick beds; FYN); the middle Miocene (middle-upper Serravallian) Cerreta-Bosco di Pietra Palomba Sandstone (ACP). This is the most

widespread formation, made up of turbidite medium-coarse sandstones of dark yellow orange color 10 YR 6/6 with characteristic diagenetic spheroids and thick and very thick amalgamated beds. These sandstones show a variable medium degree of cementation in the rock mass. Furthermore, there are pyroclastic and alluvial deposits. The former consists of juvenile ashes, ignimbrite deposits and polymictic heterometric sandy conglomerates with ash levels of the middle-upper Pleistocene (DPI). The alluvial deposits include three units. 1) The polymictic heterometric gravels and phytoclastic travertines (D’Argenio & Ferreri, 1987, 1988; D’Argenio et al., 2013) or calcareous tufa (Pedley, 1990, 2009, 2014; Ford & Pedley, 1996; Capezzuoli & Gandin, 2004; Gandin & Capezzuoli, 2008; Gandin, 2013; Capezzuoli et al., 2014; Imbriale, 2014) of white N 9 and very light gray N 8 color, characterized by wavy and radiated structures, plant fragments of encrusted macrophytes, porosity, and scarcely evident bedding (TRV) of the middle-upper Pleistocene, that form a suspended terrace on the current valley bottom. 2) The polymictic heterometric gravels with poor sandy silty matrix, consisting of pebbles of marly and siliceous limestones, and calcarenites of light gray N 7 and dark gray N 3 - N 4 color with predominantly lamellar and spheroidal shapes, referred to the upper Pleistocene-Holocene terraced deposits (at) of the actual valley bottom. 3) The Holocene-Actual similar deposits (b) (Giannandrea, 2004; Istituto Superiore per la Protezione e la Ricerca Ambientale—Servizio Geologico d’Italia, in print-a). The electrical resistivity tomography, performed on the alluvial deposits according to the 64 m long trace A - B in Figure 5(a), highlighted 4 electro-layers (Figure 5(b)). The section of Figure 5(b) shows that the first layer, whose base is indicated by the wavy yellow line, is characterized by resistivity values of 20 - 70 ohm and an average thickness of 1.50 m. The second layer, delimited by the black line, has resistivity values of 100 - 600 ohm and an average thickness of 2 m. The third layer, whose base is indicated by the line with white dots, shows resistivity values of 10 - 70 ohm and an average thickness of 6 m. The fourth layer is characterized by resistivity values greater than 600 ohms. Therefore, the first and third layers are attributed to gravels, the second layer to silty sands, the fourth layer to the ACP Sandstone. Furthermore, the section of Figure 5(c) shows that the alluvial succession consisting of gravels-silty sands-gravels has a lenticular geometry and its thickness at the top of the ACP Sandstone is less than 2 m in proximity and under the arch 2.

The tectonic setting (Figure 3 and Figure 4) to the left of the Ofanto River shows bed attitude of the ACP Sandstone dipping 20˚ - 45˚ towards SW and overturned beds dipping SW 70˚, forming an inclined syncline with northeastern vergence, while to the right of the river the bed attitude is dipping 20˚ - 35˚ towards SW forming gentle folds. The two structures to the left and right of the river are in contact by a SW-NE oriented normal fault. A second NNW-SSE oriented normal fault marks the contact between the ACP Sandstone and the succession consisting of AVR - AVR₁ - FYN (Figure 3 and Figure 4).

The section of the valley of the Ofanto River is about 50 m wide and the slopes, free of landslides, are inclined 26˚ to the left and 10˚ - 20˚ to the right of the river (Figure 4). In particular, it should be noted that the current incline (20˚) of the right slope in the bridge area (Figure 4) decreased due the works of excavation carried out on the ACP Sandstone for the construction of the national road SS 401 dir and its connection with the bridge.

In addition, the hydrogeological and seismic hazards of the study area are very high (Ippolito & Paganelli, 1984; http://www.difesa.suolo.regione.campania.it/ Vallario, 2001). The former hazard is due to: 1) sometimes impressing landslides, particularly in the very extensive areas characterized prevailingly by the Ruvo del Monte Synthem and subordinately the Varicolored Clays Formation; 2) widespread erosive phenomena caused by surface waters that are washed away and channeled along the streams flowing with high gradients in the hydrographic network of the Ofanto and Ufita rivers (Figure 1). The seismic hazard of Aquilonia, in whose territory the POB is included, and Monteverde (Figure 2) is classified in Zone 1, ie the most dangerous, characterized by acceleration index (ag) > 0.25 with a probability of being exceeded equal to 10% in 50 years (http://www.lavoripubblici.regione.campania.it/). The earthquakes of July 23, 1930, and November 23, 1980, with a magnitude, respectively, of 6.67 and 6.81 (https://www.ingv.it/), affected the Campania and Basilicata Apennine, causing many deaths and damages to small towns and locally to some infrastructures. Due to the earthquake of July 23, 1930, Aquilonia was rebuilt in an area about 2 km southwest.

The geological and geomorphological setting, the historical data from the archives, the description of the current state of the POB, and the materials used for its construction suggest the following main topics as crucial points for the POB origin: 1) the construction techniques of Roman bridges in Campania; 2) the modifications of architectural and structural elements of the bridge over time; 3) the dating of the bridge; 4) the presence of remains attributable to a Roman age bridge in the area of the SVB, in relation to the layout of the old Appian Way.

The discussion of all the data of the POB allows us to propose the following conclusions.

Structural elements,technique,period of construction of the bridge. The masonry bridge (pons lapideus) consists of 18 OASEs (the northwestern abutment, the arches 2 and 3, their relieving arches and piers, the spandrel walls of the arch 3, and the direct foundations), 12 RASEs (the spandrel walls of the arch 2, the buttresses, two cutwaters), 1 MASE (the southeastern abutment), and 4 RCASEs (the arch 1, the roadway, and the parapet walls). In addition, there are the four RDB pre-stressed reinforced concrete beams between the southeastern abutment and the arches 2 and 3, indicated as AASEs. The OASEs are built using the technique of the opus quadratum and opus incertum. Therefore, based on the technique of opus incertum, and taking into account the examples of bridges with this type of masonry located in Lazio and Marche (central Italy), Campania (southern Italy), and at Pontaujard, Montbrison-sur-Lez Villeperdrix and Pont-de-Barret, Drôme sur le Roubion in France, the dating of the bridge can be referred to the period between the II and the I century BC.

State of conservation of the bridge. Despite the restoration, consolidation and reconstruction of some architectural and structural elements, the original ones (OASEs) are still fairly well preserved.

Classification of the bridge according to the number,profile, width of arches. The bridge consists of three round arches with diminishing light from arch 1 to arch 3.

Suitability of the site for the construction of the bridge. For the design of a bridge that crosses the Ofanto River between Conza della Campania and the SVB, the most suitable site is the one where the POB was built. In fact, the river valley is about 50 m wide, the slopes made up of the ACP Sandstone are free of landslides and a very good substrate for the bridge foundations, while in the area of the SVB the river valley not only is wider (about 150 m), but its slopes, which include the Varicolored Clays Formation, are subject to frequent and massive landslides.

Importance of the bridge. The masonry bridge shows the following characteristics: considerable dimensions, original longitudinal profile with asymmetrical curvilinear trend, three round arches, piers with a thickness of 4.30 m, roadway 103.60 m long and 4.30 m wide, which could allow the wagons to transit in two ways. Therefore, the bridge had to be at the service of a very important public road.

In conclusion, the present research is allowed to achieving three goals:

➢ to establish, based on the geological and geomorphological setting, that the most suitable site for the construction of a bridge over the Ofanto River between Conza della Campania and the SVB in Roman times is the one where the POB was built;

➢ the POB is identified with thePons Aufidi in agreement with the southern layout of the old Appian Way between Mirabella Eclano (Aeclanum) and Venosa (Venusia), which is the shortest, most convenient in terms of design and construction, and therefore the most reliable. Consequently, the hypothesis of the northern layouts, which cross the Ofanto River by the SVB, is no longer sustainable;

➢ the construction technique of the POB helps to improve the knowledge of Roman bridge engineering, particularly in Campania.

In order to improve the state of conservation of the POB, we suggest to the Archaeological Superintendence of Campania, territorial authority responsible for the management of archaeological assets, to prepare a study aimed at maintenance and safeguard of the bridge by some suggestions.

➢ Periodic checks of the following elements: conditions of stone materials and masonry mortar with interventions aimed at restoring deteriorated parts, weed and climbing vegetation that covers extensive surfaces of the structures, thermal and hydrological variations, washing away action, fire, salt efflorescence, chemical aggression from pollutants, weight of bearing walls and accessory parts, transit of vehicles, ordinary and accidental hydrodynamic flow of the river, sinking and undermining of the setting planes, subsidence of foundations, seismic effects. In this regard, the weight analysis is suitable to evaluate the weights of the load-bearing walls and accessory parts. Such an investigation, carried out by the core drilling and the determination of their volumes, specific weights and centers of gravity, is particularly significant for the check of limit conditions of the bridge.

➢ Because the bridge is located in an area with high seismic hazard, the non-destructive sonic tests of materials are aimed at modeling the structural behavior for seismic action, which requires the knowledge of the mechanical distribution of deformation and resistance of materials, in particular of the walls.

The research was supported by the Associazione Nazionale per gli Interessi del Mezzogiorno d’Italia (ANIMI). The authors are grateful to Armando Marano and Angelo Pizzella who produced the images of the bridge taken by the drones; Giovanni Savarese and Raffaele Miranda who took care of the graphics of the figures; Celestino Grassi² for the useful discussion on the structures of the bridge.

The authors declare no conflicts of interest regarding the publication of this paper.

Chiocchini, U., De Piano, M., Gaeta, M., Pagliuca, E., Polzone, N., & Sarmento, F. (2021). Geoarchaelogical Study of the Roman Pietra Dell’Oglio Bridge at the Service of the Old Appian Way, Campania, Southern Italy. Archaeological Discovery, 9, 223-258. https://doi.org/10.4236/ad.2021.94012