## 4 Discussion
These are coastal sites embedded in the urban environments of the modern towns that have historically developed nearby [23]: Susah, Ad Dirsiyah, and modern Tocra, respectively (Figure 10b-d). Figure 10: (**a**) Synoptic view of Cyrenaica (Libya) and the archaeological sites of Tocra, Ptolemais, and Apollonia through a multi-temporal mosaic of cloud-free Sentinel-2 images acquired from 29 July 2015 to 4 October 2015. The zoomed views on (**b**) Tocra, (**c**) Ptolemais, and (**d**) Apollonia. Block features and the proximity of the modern towns are clearly visible. Copernicus Sentinel-2 images © 2015 European Space Agency—ESA. The synoptic view achieved with only two Sentinel-2 images allowed us to highlight slightly different situations in these three sites. In 2015, in Tocra and Apollonia, recent urbanisation was not immediately affecting the archaeological sites, although this was already an anthropogenic process that was apparently re-shaping the wider landscape (Figure 10b,d). In particular, Susah expanded through one large project of urban development in the south-east and through new roads and building blocks in the south-west, but no new block features were developed at that time in the proximity of the archaeological site of Apollonia (Figure 10d). However, some properties were already built very close to the southern boundary of the site (see also Figure 11d). Similarly, there was no evidence of new blocks built in the proximity of the ruins of Tocra in 2015, but outside the modern town, several road-blocks had already appeared (Figure 10b). Conversely, in mid-2015 urbanisation was already affecting the archaeological site of Ptolemais (Figure 10c). A new road-block enclosing land lots had been already created close to the western boundary of Ptolemais, in a portion of land west of the Wadi Khambis that was previously vacant (see also Figure 11b). Other road-blocks had been laid down along the coast, north-east of the site, beyond the Wadi Ziwana (Figure 10c). Figure 11: The condition on the ground in (**a**) Tocra, (**b,c**) Ptolemais and (**d,e**) Apollonia as captured by Sentinel-2 in 2015 versus 2017. (**a**) New block features (yellow polygons) are visible around the modern town of Tocra; (**b,c**) no change is detected over the existing block feature close to Ptolemais; (**d,e**) the development of previously vacant land lots along the southern boundary of Apollonia (yellow polygons). Copernicus Sentinel-2 images © 2015–2017 European Space Agency—ESA. By analysing Sentinel-2 data until the end of 2017, no further changes were found within the footprints or along the boundaries of the archaeological sites of Tocra and Ptolemais (Figure 11a-c). In particular, the urban sprawl continued south and east of the modern town of Tocra (Figure 11a), so only continuous monitoring could show the future direct impacts on heritage conservation. In Ptolemais, the block feature that was observed in 2015 (Figure 11b) did not appear to have been populated yet with buildings or farming activities in 2017 (Figure 11c), so it had still not developed into a mature stage according to the cycle discussed in Section 3.3 (see also Figure 5). Conversely, we detected clear changes in the surface reflectance along the southern boundary of Apollonia that matched with the development of previously vacant land lots from late 2015 to mid-2017 (Figure 11d,e). Therefore, we could update our assessment of the degree of exposure of these three sites to the impacts due to urban expansion and land use changes.