What does it mean to pile pebbles on the roadside in Tibet?

These stone piles are called Mani piles, and they are called "Duobang" in Tibetan, which means built stones.

Tibetans believe that stones are spiritual, so they will pile Mani stones at intersections, lakes or mountains to pray. When you pass by the Manifold, turn clockwise and fill a stone, so that the longer it takes, the bigger the Manifold will be.

Extended data:

"Multi-gang" can be divided into "multi-gang" and "multi-gang". "Flower gangs prevent filth and disasters" are mostly located at the end of the village. The stone pile is huge and the upper part is stepped. There are scriptures to stop filth, eliminate disasters and pray for blessings, as well as grains, gold and silver jewelry and spears. "Anti-evil flower gangs" are mostly distributed on roadsides, lakes and crossroads. The stone pile is small, conical and without steps, and the right pile contains anti-evil mantras.

Mani stone is a traditional Tibetan folk art, most of which are engraved with six-character mantra, insightful eyes, statues and various auspicious patterns in order to eliminate disasters and seek happiness. Mani stone can be composed of Mani pile or Mani wall, which can be seen in mountains, rivers, lakes and intersections all over Tibet. On auspicious days, people simmer mulberries, add stones to the Mani heap, touch it with their foreheads devoutly and pray constantly.

References:

Manidui-Baidu Encyclopedia