Cairns have been used for many purposes throughout history, including:

* Navigation: They act as landmarks and guide travelers, especially in mountainous areas.

* Memorials: Some are built to honor loved ones or mark important events.

* Religious purposes: Some cultures believe cairns have spiritual significance.

* Modern use: In some areas, cairns are used to mark trails and help prevent erosion.

It's important to note that in some areas, building cairns is discouraged as it can disrupt the natural landscape and confuse other hikers.