The decorative and epigraphic elements of sculpture and inscriptions have been extensively studied (RIB I; RIB III; Keppie and Arnold 1984), but less attention has been paid to their production and geological provenance. Where this has been done it seems predominantly local, but there are instances of imported stone (marble, also limestone) and enigmatic material (eg the white sandstone of the Cramond lioness) which may have been deliberately sought out (Hunter and Scott 2002; Hunter and Collard 1997). The Ingliston milestone (Maxwell 1984c), for instance, seems to be a non-local stone.
Stone was also used in a variety of other facets of life. The use of quernstones is perhaps the most obvious, but a range of other stone objects was also used, such as mortars, whetstones, or jewellery in jet or related materials. There has been little attempt to extract information from these (see Allason-Jones and Jones 1994 for what can be achieved with black organic-rich stones). Yet, to take querns as an example, while the bulk was supplied from imported stones from the Rhineland, there was also a range of other quern types, many using more local styles (including Iron Age traditions) and sources; this merits fuller research (e.g. MacKie 2007).
How extensive was decorative stone-carving among auxiliary units? Did it take place at every fort? What was the distribution of carved stone on a site - who had access to it, and who was the imagery intended to impress? What stone resources were exploited for this? (A question intimately connected to stone for building purposes; see section 5.3).
Research into stone tools and their raw materials' provenance is required. Querns would be a particularly good topic, looking beyond the Rhineland querns to the use of other local or imported stones.