A #cairn is a human-made pile (or stack) of stones. The word cairn comes from the Scottish Gaelic: càrn [ˈkʰaːrˠn̪ˠ] (plural càirn [ˈkʰaːrˠɲ]). .
Cairns are used as trail markers in many parts of the world, in uplands, on moorland, on mountaintops, near waterways and on sea cliffs, as well as in barren deserts and tundra. They vary in size from small stone markers to entire artificial hills, and in complexity from loose conical rock piles to delicately balanced sculptures and elaborate feats of megalithic engineering. Cairns may be painted or otherwise decorated, whether for increased visibility or for religious reasons.