A ring cairn is a prehistoric ritual monument comprising a circular bank of stones up to about 20m in diameter surrounding a hollow central area. The bank may be kerbed on the inside, and sometimes the outside as well, with small uprights or laid boulders. Within the central hollow there may be charcoal-filled pits and sometimes burials, occasionally under small mounds.
Ring cairns are mainly found in upland areas of England, and are mostly discovered and authenticated by fieldwork and ground-level survey. Some ring cairns are large enough to be visible on aerial photographs, although surface checking is usually needed to authenticate interpretation. The erosion and/or robbing of other classes of round barrow (esp. bowl barrows) sometimes makes them hard to distinguish from ring cairns. Tor cairns may also be confused with ring cairns because of the natural or earthfast boulders that sometimes occur within ring cairns; tor cairns have larger natural outcrops which lie in the centre of the site. Other possible sources of confusion include stone hut circles, stone circles, clearance cairns, and small stone-walled enclosures of various classes.
Specifically excluded from the definition of ring cairns are circular structures with a small infilled central space (these are defined as platform cairns) and embanked stone circles which have a ring of stones set into or more usually at the outer edge of a bank and have an entrance gap in the circuit. It may also be noted that circular banked enclosures around the central burials beneath some types of bowl barrow, fancy barrow and bell barrow are components of those monuments and should not be considered as ring cairns unless they can be identified as quite separate phases to the site.
Ring cairns are traditionally interpreted as ritual monuments of early and middle Bronze Age date. The exact nature of the rituals concerned is not known, but burial and rites in celebration of the dead seem to have been undertaken at some examples. Interpreted as such, the function and role of ring cairns may duplicate or overlap that of other broadly contemporary monuments, for example tor cairns, pond barrows, and some kinds of fancy barrows.