A tor cairn is a prehistoric ceremonial site comprising a circular bank of stones, sometimes set on a platform, which encloses and in some cases partly covers a centrally located large natural outcrop of rock, usually a tor or a very large grounder. The overall diameter of tor cairns ranges from about 12m to over 30m, the hieght of the bank from 0.5m to about 4.0m. There is usually an entrance into the enclosed area, and pits dug into the ground within the enclosure. Cultural debris including flint tools, pottery, quartz pebbles, and bronze weapons and ornaments have been found scattered within the enclosed areas during excavations.
Tor cairns are recognized as upstanding features from surface surveys and aerial photography. In both cases the places to search for traces of this class of site are limited by the available tors and natural rock outcrops which form the central features. It may be noted, however, that tor cairns with central rock outcrops of modest size are much less easy to recognize that those with large rock outcrops because in the former the rock features may have become covered by soil and turf. Possible sources of confusion when identifying tor cairns are ring cairns, clearance cairns, natural accumulations of clitter around a rock exposure, and quarrying debris. In most cases the authentic tor cairns can be differentiated by the regular plan of the ring bank and the fact that an open area exists between the inner edge of the ring bank and the central rock feature.
Specifically excluded from this definition of tor cairns are various classes of round barrows, especially bowl barrows and fancy barrows, that contain within the matrix of their mounds one or more natural rock outcrops or grounders. With tor cairns the natural outcrop is always fairly central to the monument and there is an open area all around it.
The function and purpose of tor cairns is not precisely known, although it may be concluded that some sort of significance or power was attached or attributed to the natural formations at the focus of each monument. Thus they may be considered as ceremonial sites which date to the early and middle Bronze Age. As such they may share functions with other similar monuments, for example ring cairns and pond barrows.