Integrated geomatic methodologies to reconstruct the ancient topography of Rome

The current urban centre of Rome is built upon up to ten metres of anthropic layers formed between the Early Bronze Age, when the Capitolium was first occupied, and the present days. These layers represent an inestimable record of the events (buildings, demolitions, collapses, fires, floods, etc.) that shaped the appearance of the eternal city. However, most of time the investigations take place near or under contemporary historical or modern structures, which made the excavations very complex from a technical point of view. One of the most complex issue become to precisely place in a common tridimensional framework the structures gradually unearthed, to compare them with the already known (and placed) ancient features (Bitelli et al., 2017; Radicioni et al., 2017). Along this line of research, starting from 2008, the Superintendence of Rome is gradually building up a webgis called SITAR (Sistema Informativo Territoriale Archeologico di Roma) (De Tommasi et al., 2012) to bring together all the archaeological features of Rome, based on the datum Roma40. The aim of this paper is to present a possible effective workflow to precisely place the ancient buildings and features using geomatic methodologies. A recent excavation in the centre of Rome will be used as a case study. The correct reconstruction of the structures unearthed during an archaeological excavation in an urban environment must integrate geometric information from various sources and certainly: a) Contemporary large scale cartographies of the urban fabric georeferenced to absolute reference systems (EPSG, 2020). b) Topographic surveys with terrestrial instruments of the current excavation area that provide the coordinates of remarkable points of the area itself; the absolute positioning of the survey is often made more complex by the reduced visibility of the sky and consequently of the GPS/Gnss constellations (Alessandri et al., 2019; Baiocchi et al., 2016; Eyre et al., 2016). c) Laser scanning surveys that provide threedimensional point clouds and corrected images that must be oriented with respect to the points of terrestrial surveys (Angelini et al., 2017). d) Photogrammetric acquisitions that, through classic or SFM models, can render the details of the excavation or the entire clouds of threedimensional points (Alicandro, 2018; Chikatsu and Takahashi, 2009; Fritsch and Syll, 2015; Guarnieri et al. 2011; Lo Brutto, 2017; Mandelli et al., 2017; Nocerino et al., 2014; Perfetti et al., 2017; Stocchi et al., 2017; Troisi et al., 2017). e) Chronicles, map drawings, diagrams, reports and photos of previous investigations in the same area, often carried out during the construction of the modern buildings; this information is generally referred to local reference systems. f) Cartographies showing three-dimensional characteristics of the area in periods prior to urbanization, usually georeferenced in reference systems that are no longer used and difficult to reconstruct (Lelo, 2020). g) Ancient cartographies, georeferenced in reference systems no longer known (e.g. the Forma Urbis Romae, fig. 1) (Cozza, 1968; Gatti, 1959).