Milestones were originally stone (granite or marble) obelisks and later concrete posts. They were widely used by the Roman Empire roadbuilders, an important part of any Roman road network when the distance travelled per day was only a few miles in some cases. The first Roman milestones appeared on the Appian way. The term continues to be used today, even though the "stones" are typically metal signs, and the distances are often measured in kilometres.
In Europe the distance measured typically starts at a city or town, as many roads were named for the towns at either end. In the US Interstate highway system the numbers usually measure the distance to the southern or western state line, while other highways use the county line as the benchmark. Often, the exits are numbered according to the nearest milepost, known as the mile-log system. Some historic and scenic routes use mileposts to mark points of interest, such as along the Blue Ridge Parkway in North Carolina and Virginia, and the Overseas Highway of the Florida Keys.
There is also a publication called The Milepost, about the Alaska Highway.
Metaphorically, milestone is used to denote reaching an identifiable stage in completion of something other than a physical journey, as in project management, world events, and the like.
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