Boundary marker

A boundary marker, border marker, boundary stone, or border stone is a robust physical marker that identifies the start of a land boundary or the change in a boundary, especially a change in direction of a boundary. There are several other types of named border markers, known as boundary trees, pillars, monuments, obelisks, and corners. Border markers can also be markers through which a border line runs in a straight line to determine that border. They can also be the markers from which a border marker has been fixed.

Source: Wikipedia