## Materials and Methods
A proof of concept on the visible bands, without further sophisticated processing of these and other bands, is expected to ease the initial uptake of Sentinel-2 by a wider spectrum of practitioners. We acknowledge though, that future research and implementation could take advantage of recently developed methods. For example, the sharpening of Sentinel-2 bands with spatial resolutions of 20 m and 60 m to a spatial resolution of 10 m, in order to obtain a full set of visible and near-infrared (VNIR) and shortwave infrared (SWIR) spectral bands with a spatial resolution of 10 m [26]. To carry out our analysis we discarded products where clouds hampered the visibility of the heritage sites. Since Sentinel-2 is an HR satellite constellation, we did not expect to distinguish small to very small features (that is, \(<\)10 m). Instead, we aimed to demonstrate that Sentinel-2 data can be used for \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Hotspot** & **Heritage Status** & **Heritage Category** & **Process** & **References** \\ \hline Aleppo (Syria) & WHS & Urban & Urban warfare & [1; 17; 18] \\ Apamea (Syria) & TWHS & Hellensitic town & Looting & [1; 19; 20] \\ Cyrene (Libya) & WHS & Greek town and cultural & Urban development & [5; 21; 22] \\ Apollonia (Libya) & - & Greek town & Urban development & [23] \\ Ptolemais (Libya) & - & Greek town & Urban development & [23] \\ Tocra (Libya) & - & Greek town & Urban development & [23] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The summary of the demonstration sites with an indication of the heritage status (if applicable); the heritage category; the type of process impacting the site conservation that is discussed in this paper; references for a historical, archaeological, and conservation introduction to the sites. Notation: WHS = World Heritage Site; TWHS = Tentative WHS. the systematic and regular screening at the site scale to identify larger single features, clusters of small features, and accumulations of progressive (small) changes that eventually manifest as new prominent surface features. For example, while individual looting features could not be resolved in the Sentinel-2 data, clusters of several adjacent looting holes are clearly detectable (see Section 3.2). We ran a multi-temporal analysis by using the full Sentinel-2 archive available for each of the demonstration sites that provides, at best, a 5-day revisiting time from one acquisition to the next. However, because Sentinel-2A was launched on 23 June 2015 and in consideration of the time needed for commissioning (that is, ~3 months from the end of launch and early orbit phase), in some cases, the earlier cloud-free images available for the demonstration sites were acquired in October 2015. We spatially analysed the Sentinel-2 stacks against ancillary data including, but not limited to site plans, maps of heritage assets, and thematic maps. In particular, for each demonstration site, we defined the T\({}_{0}\) time reference, against which we detected the new features based on either their textural or surface reflectance properties. For this purpose, we applied the state-of-the-art change detection techniques currently used across the specialist community (for example, Reference [27]). In practice, for each pair of Sentinel-2 images acquired at T\({}_{n-1}\) and T\({}_{n}\), the surface reflectance at bands B4, B3, B2 and the textural properties were compared and clusters of pixels indicating hotspots of change were highlighted and zoned through a conversion to polygons. We interpreted the observed features following the same standard mapping methodologies that are commonly used by research teams and practitioners to assess the condition of a heritage site using optical satellite imagery [3; 5; 6; 19].