Through the application of a wide range of geophysical survey techniques, a very complex, multi-period set of connected features were uncovered that has caused scholarship to re-evaluate the place that Cruachan held in Iron Age and medieval Ireland. I say this because, as recently as 1994, one of the prime indicators or characteristic features of a 'royal' site, such as Emain Macha, Tara, or indeed Rathcroghan, was the presence of a prominent ritual 'enclosure'. The feature was deemed present at all of the traditional royal sites, except for Cruachan (Raftery, 1994, p. 70). Through the application of a magnetic gradiometry survey on the mound and it's vicinity, as well as analysis of aerial photographs from as early as 1983, the presence of a very large enclosure was uncovered, 360m in diameter, around Rathcroghan Mound. As well as encompassing the mound itself, it also held a number of other features, some of which can be readily identified in the below image.
Rathcroghan Mound & 360m enclosure, magnetic gradiometry image (Waddell, Fenwick, Barton 2009, Fig. 5.6)
These include a feature which surrounds the immediate environs of the mound, an attached avenue, a seemingly earlier feature within said avenue, as well as a smaller, more northern parallel monument, with similarly aligned avenue. All of this points to a protracted period of use, as well as some reinterpretation of the environment during its period of use.