*2.2. Survey Methods*

The monuments have been surveyed onsite whenever possible (some are of difficult or no access). However, they are in any case very difficult to measure due to vegetation, fences, and to the fact that the sides are not always clean. Therefore, we took advantage of the fact that the area is well

covered by satellite imagery (both on Google Earth and Bing), with a resolution which is more than sufficient to measure the average sides and average azimuths of the mounds. Another problem that satellite imagery is helpful in solving is that of the ancient horizon. Indeed, the horizon visibility today is very poor—due to pollution—even when the horizon itself is clear of buildings; moreover, sometimes, modern buildings are actually present. Using satellite tools, it is instead possible to establish whether monuments had mutual intervisibility in the past or not. All in all, the available images—in many cases, the historical archive of Google Earth contains more than one image with a sufficient resolution—were extracted and measured with AutoCAD for length of the sides, orientation, and directions of visibility towards other monuments. The results were mediated in the presence of more than one image. Errors have to be expected, of course, but on account of the high quality of the images and of the low projection error associated with them, the intrinsic error expected from this kind of measurement is quite low, so Google Earth is a quite useful tool for this kind of investigation [7,8]. Unfortunately, however, the original heights of the mounds (certainly greater than the current ones) were impossible to determine because the summits have deteriorated considerably (see, e.g., Figure 2).

**Figure 2.** The huge burial mound of Maoling, the tomb of emperor Wu of Han, looks like a smoothed, natural hill. It is, instead, fully artificial: a pyramid made of hard rammed earth. (Photograph by the author.)

#### *2.3. Methodology*

The approach presented here is that of cognitive archaeology, as developed in the last 30 years or so [3–6]. In a nutshell, it is an approach to the material relics of human past which aims at describing them as objects that had their primary cultural existence as "percepts" in topological relation to one another. They thus fitted within the cognitive schemes of their creators, and can be fully understood—that is, not only "functionally" understood—only if such schemes are also studied and, as far as possible, understood as well.

A particularly interesting case in such a context is that of sacred landscapes; that is, natural landscapes in which monuments were built in accordance with rigorous criteria, usually connected with power and religion (for a general approach to the relationship between traditional built environments and perceived meaning, see [9–12]). In the case of such landscapes, indeed, the cognitive approach turns out to be extremely effective; for instance, in the study of ancient Egyptian Necropolises [13–16]. In such studies, the use of satellite imagery reveals itself as being particularly useful. In fact, it allows to establish the mutual relationships between monuments also in the presence of evolving dynamics of the built features of the landscape.
