A stone serving the same purpose as a milepost.

stone post at side of a road to show distances

a marker in your schedule

a sort of marker that tells you where you are while traveling

A stone block set along a road, specifying the distance (in Roman miles) from a fixed starting point on the road. It is a typical find of the Roman period, generally inscribed with the name of the ruler during whose reign the road was built or repaired.

A milestone or kilometre sign is one of a series of numbered markers placed along a road at regular intervals, typically at the side of the road or in a median. Milestones are constructed both to reassure the traveller that the proper path is being followed and to indicate distance travelled, or the remaining distance to the desired destination. They are alternatively known as a mile marker, milepost, or mile post (sometimes abbreviated MP), notably in the United States.