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 pillars, 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.
The word boundary_marker is 'all-encompassing', because a boundary_stone is a boundary_marker, but not all boundary_markers are IN STONE.
Boundary markers, traditionally, were often made of stone, but later many have been made with concrete or a mixture of materials. They are typically placed at a notable or especially visible point. Many are inscribed with relevant information such as the abbreviation of the boundary holder and often a date.