A multiscale geoarchaeological approach from the Laurentine shore (Castelporziano, Lazio, Italy)

Abstract

The ability to investigate meaningful geoarchaeological questions is driven by appropriate scale-process focus fundamentally informing sampling strategies. This in turn, is driven by site-specific characteristics such as topography, sedimentology, geochemistry and climate. The Laurentine Shore is the Roman-period palaeo-shoreline preserved up to 1 km inland of the modern coastline of the Tiber Delta at the southern distal end. Mid- to late-Holocene progradation of the Tiber Delta linked to sediment supply in the context of changing relative sea level drives the macro-scale (103+) development of the region. Archaeological remains preserved within the Presidential Estate of Castelporziano must be interpreted within this macro-scale context. Using a multiscale, transect-based approach, SAAD-IRSL luminescence dating of relict foredune ridges has provided an age model constraining the development of the Tiber delta during the late Holocene. Both radiocarbon (Giraudi et al., 2009) and luminescence chronologies of dune ridge phases are in good agreement. Due to the protected status of the Castelporziano Estate the Holocene coastal dune topography is better preserved than at the central delta area and two additional phases of dune ridge formation are observed. Four macro-scale phases of delta progradation are recorded by the dune ridge record with increased mean rates of progradation observed during the Roman period and within the last 500 years. On the meso-scale (102) the high-status villas on the Laurentine Shore, and the Vicus Augustanus that serviced the villas are specifically located on the Roman-period shoreline. The timing of settlement (from around 2050 BP, i.e., 1st century BC) occurs during a pronounced Tiber delta progradation phase. Within this macro-scale context issues of sediment supply, frequency of Tiber flooding and the expression of shoreline advance at the Laurentine Shore have important meso-scale consequences for the development of the archaeological sites. It is likely that during the 2-phase development of the Vicus Augustanus that shoreline progradation was an observable phenomenon on decadal to multi-decadal timescales. Indeed the second, major seaward construction phase of the Vicus Augustanus likely occurred upon land that did not exist during the first phase, directly linked to delta progradation and the macro-scale processes acting upon the development of the site including anthropogenic activity in the Tiber catchment during the Roman period.