Adam Clarke on 2 Samuel 18:17

And laid a very great heap of stones - This was the method of burying heroes, and even traitors, the heap of stones being designed to perpetuate the memory of the event, whether good or bad. The ancient cairns or heaps of stones, in different parts of the world, are of this kind. The various tumuli or barrows in England are the same as the cairns in different parts of Ireland and Scotland. In the former, stones were not plenty; hence they heaped up great mounds of earth.