New insights into urban planning of Caricin Grad: The application of modern sensing and detection methods

Abstract
Caricin Grad, Justiniana Prima, urban planning, fortification, settlement, aerial photography, geophysical surveys, LiDAR, photogrammetry, excavations, GIS. Thanks to the application of modern non-destructive sensing and detection methods, in recent years a series of new data on urban planning in Caricin Grad was obtained. For the most part, the current research programme studies the Upper Town?s northern plateau, wooded until recently and hence the only previously unexplored unit of the city. In the course of this programme, the classical research method - the excavations started in 2009 - is for the first time combined with the systematic application of airborne and terrestrial sensing and detection techniques. The analysis of historic aerial photographs and topographic plans proved to be very useful as well. Along with them, LiDAR-derived DTMs, photogrammetric DEMs, different geophysical and orthophotographic plans are stored in the GIS database for Caricin Grad and the Leskovac Basin. In this way almost 80 percent of the plateau area was defined, and the obtained plan is hypothetical only to a small extent, which particularly refers to the unexcavated northern rampart of the Upper Town. Each source provided relevant information for the reconstruction of both the rampart and the settlement, which points to the value of a holistic approach to documentation from various dates. The first source to be studied were archival aerial photographs of Caricin Grad from 1938 and 1947 (Figs. 1, 2.1). The latter one was originally processed by Aleksandar Deroko and Svetozar Radojci}, who drew the plan of the town after it, labelling the unexplored Upper Town?s northern plateau as ?a probable habitation area?. The route of the northern rampart was aslo rather precisely determined by the authors (Fig. 2.2). Recently, these photographs were rectified and georeferenced in the GIS. The 1938 shot reveals the position of some towers as well, and it is also indicative of the way of construction of certain buildings. From the spatial layout of whitish zones, originating from mortar scattered along the slope, it can be deduced which buildings were constructed in opus mixtum - the horreum and the so-called Building with Pillars east of it. Traces of mortar can be observed along the route of the rampart too. These archival images are particularly important because they record the topography of the site before it was filled with heaps of earth from the excavations. The topographic mappings of this area were conducted in 1981 and 2006 (Fig. 3). The first plan was drawn after an airborne stereophotogrammetric survey of Caricin Grad, and in 2006, after the wood was cut down, this whole area was surveyed with the total station, with a density of nine points per square meter. This survey also resulted in a 3D terrain model (Fig. 3.2) indicating the layout of the buildings, which was to be proved by geophysical surveys and archaeological excavations. In the course of the Serbian-French reaearch programme, in 2007 geomagnetic surveys were carried out by Alain Kermorvan of the University of Tours. Thanks to the application of this method the remains of collapsed stone structures could be observed, and in 2015, in cooperation with the Roman-Germanic Central Museum, Mainz, and the Ludwig Boltzmann Institute from Vienna, the middle and eastern parts of the plateau were scanned with GPR (Fig. 4.2). Precise plans of the buildings were obtained in the areas in which LiDAR scanning and photogrammetric and geomagnetic surveys failed to produce clear images. Within the framework of the ArchaeoLandscapes Europe project, in 2011 we managed to organise an airborne LiDAR survey of the wider area of Caricin Grad. With its density of some 20 points per square meter, this scanning proved to be crucial for our comprehension of the town. The standard DTM provided numerous important data, especially its version calculated in the focal statistics function of the ArcGIS software package (Fig. 5. 1-2). These models show not only the route of the Upper Town?s northern rampart, the position of its towers and the layout of the buildings, but also the line of the Outer Town?s western rampart. Visible only in the DTM, this entirely new aspect of the Caricin Grad fortification has been attested by the excavations. Highly important plans of the town, and of the northern plateau of the Upper Town in particular, were obtained by UAV photogrammetric surveys. The first drone survey was conducted in 2014 within the scope of the same project. It resulted in a cloud with up to 1,600 points per square meter (Fig. 6.1-2). Unlike the LiDAR technology, photogrammetry cannot penetrate vegetation; therefore the preliminary clearing of the ground proved to be a most important step. After the 2015 campaign was finished, the excavation area in the Upper Town was documented again in the same manner. Regular photogrammetric surveys make possible the control of the works and reliable visual monitoring of the progress of exploration (Fig. 9). After the wood was cut down in 2006 and enormous heaps of earth from twentieth-century excavations and restoration works were carefully removed by machinery in 2008 and 2010, without disturbing the original layers of debris, wide excavations could begin. At first only the humus layer was removed from fifteen-meter squares, which was followed by technical drawing. In 2009 and 2010 we did not explore the debris or the cultural layers (Fig. 7.1-2). The additional two squares were opened and documented in the same fashion in 2011, when previously recorded buildings 11 and 15C were explored in detail, together with the part of the corridor between them where a bread oven was found. These buildings were oriented south-north, cascading along the mild slope towards the northern rampart of the Upper Town. Fragments of pithoi and carbonised fruits were found in the buildings, allowing for an economic interpretation. Judging by...