According to Wikipedia a cairn is: “a human-made pile of stones. The word cairn comes from the Scottish Gaelic: càrn. Cairns have been and are used for a broad variety of purposes, from prehistoric times to the present.”
One can see many cairns on the north shore of Lake Superior. We spent a few nights camping up near Tofte, MN and went hiking in near-by state parks and along the rocky shore. Wherever there were rocks there were cairns. A local woman told me Native Americans used to build cairns as trail markers.
We made our own cairn near the waters edge where we placed our camp chairs to sit and listen to the waves and read our books for an afternoon. We were able to balance eight small stones.
Another day I witnessed a little boy, about 2 years old, walking along, happily knocking over a cairn as he passed by. It’s a good thing we are not relying on cairns for navigation these days.