Baelo Claudia is located in the actual province of Cádiz and ancient Roman province of Baetica, on the conventus gaditanus in Bolonia Bay where it overlooks the Atlantic Ocean. It is within the axial zone of the Gibraltar Strait, the westernmost termination of the Mediterranean Alpine Chain of the Betic Mountainus system. The area is topographically dominated by small isolated mountains that trend NE and reach a maximum elevation of 457 m (e.g., the Sierra de la Plata). The fluvial drainage is essentially seasonal.
The local geology at Baelo Claudia is dominated by Upper Cretaceous to Lower Miocene sandstone turbidites of the Aljibe Series. Thus, the most common lithologies surrounding the settlement are Aljibe sandstone, breccia limestone, bioclastic limestone, marly calcarenites, marls, and micaceous red clays (ITGE, 1990). In addition, underlying the site are softer plastic marly clays of the Cretaceous-Eocene Bolonia Unit, upon which the Roman city was founded.
The surrounding environment of Baelo is marked by the transition between slopes, Pleistocene marine terraces, and littoral landforms such as dunes and Holocene spit bars. Previous geoarchaeological research has contributed to the reconstruction of the ancient geomorphology of the Roman landscape through geotechnical studies and geophysics (Dardaine et al., 1983; Vorsevi, 1993, 1995; Borja, Martínez, & Troya, 1996; Alonso Villalobos et al., 2003; Alonso-Villalobos et al., 2003; Alonso et al., 2007). These works demonstrate that the geomorphological setting has changed substantially since Antiquity: a fluvial system around the city was composed not only of the present-day channels Arroyo de las Viñas and Chorrera Jiménez, but also presently abandoned channels of the Arroyo del Pulido and others (Alonso Villalobos et al., 2003). This drainage was more widespread and integrated in the past as shown by geotechnical coring reveals. Terminal river systems were comprised of small fan deltas and marshes parallel to the shoreline. Finally, an ancient lagoon east of the city was formed by a spit bar and represents the latest depositional geomorphological event (Dardaine et al., 1983). Well-log data indicate that the dark-silts of the lagoon were buried by a 4 m thick colluvial sequence composed mainly of clays (Silva Barroso et al., 2005). The spit-bar systems and lagoon-clays are dissected by the present drainage network (Gracia & Benavente, 2000), which has changed the seasonal river courses as historical aerial photographs demonstrate.
Baelo Claudia was founded in the 2nd century BC according to numismatic evidence, although the oldest known buildings date back to the Augustan period (end of 1st century BC to beginnings of 1st c. AD). This small stipendiaria city located in the Baetica province obtained the privileged status of Roman municipality, most probably under the government of Claudius (Sillières, 1995). From that moment, the city gradually became endowed with a monumental center according to the new administrative and management needs. Between the 2nd and 3rd centuries traces of ruins of some buildings have been found, which may relate to seismic activity and building collapse (Silva Barroso et al., 2005; Grützner, Reicherter, & Silva, 2010). From then on, the city's urbanism was transformed, and human occupation continued until the end of the provincial administration in Hispania – and beyond – at the end of the sixth century and the beginning of the seventh century, in the Visigoth period. It is at this moment when Baelo is finally abandoned (Brassous et al., 2017).
The history of the investigations begins with the first excavations between 1917 and 1921 led by two of the great pioneers of archeology in Spain: P. Paris and G. Bonsor (Paris et al., 1923, 1926). After a period of abandonment related to the Second World War and the Spanish Civil War, archaeological investigations were resumed between 1966 and 1990 under the direction of different archaeologists of the Casa de Velázquez (Domergue, 1973; Dardaine et al., 1983; Didierjean, Ney, & Paillet, 1986; Bost et al., 1987; Bonneville, Dardaine, & Le Roux, 1988; Bourgeois & Mayet, 1991; Bonneville et al., 2000; Fincker et al., 2008; Sillières, 2013). Additionally, other projects have focused their attention on specific topics (Arévalo González & Bernal Casasola, 2007; Prados Martínez & Jiménez Vialás, 2015). After decades of archaeological research, the walls are almost completely known as well as the forum, the theater, some public baths, and an industrial district dedicated to the processing of goods of the sea. Other remains occur outside of the city, including the necropolis, suburban thermal baths, and the system of water supply that involves two aqueducts.
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