A milestone is a numbered marker placed on a route such as a road, railway line, canal or boundary. They can indicate the distance to towns, cities, and other places or landmarks like mileage signs; or they can give their position on the route relative to some datum location (a zero milepost). On roads they are typically located at the side or in a median or central reservation. They are alternatively known as mile markers (sometimes abbreviated MMs), mileposts or mile posts (sometimes abbreviated MPs). A "kilometric point" is a term used in metricated areas, where distances are commonly measured in kilometres instead of miles. "Distance marker" is a generic unit-agnostic term.

Milestones are installed to provide linear referencing points along the road. This can be used to reassure travellers that the proper path is being followed, and to indicate either distance travelled or the remaining distance to a destination. Such references are also used by maintenance engineers and emergency services to direct them to specific points where their presence is required. This term is sometimes used to denote a location on a road even if no physical sign is present. This is useful for accident reporting and other record keeping (e.g., "an accident occurred at the 13-mile mark" even if the road is only marked with a stone once every 10 miles). Distance markers are typically written only to integer values (sometimes with a single significant figures), often with the unit name or symbol before the number, as in "mile x" or "kilometre y", for example, "mile 317" or "kilometre 510".

Miliarium (Classical Latin: [miːllɪˈaːrɪ.ũː ˈau̯rɛ.ũː]) were originally stone obelisks – made from granite, marble, or whatever local stone was available – and later concrete posts. They were widely used by Roman Empire road builders and were an important part of any Roman road network: the distance travelled per day was only a few miles in some cases.^{[citation needed]} Many Roman milestones only record the name of the reigning emperor without giving any placenames or distances. The first Roman milestones appeared on the Appian Way. At the centre of Rome, the "Golden Milestone" was erected to mark the presumed centre of the empire: this milestone has since been lost. The Golden Milestone inspired the Zero Milestone in Washington, D.C., intended as the point from which all road distances in the United States should be reckoned. Odometers were used to measure the Roman milestone spacing, most likely based on Ancient Greek technology.^{[citation needed]}

A mile-marker monument, the Milion, was erected in the early 4th century AD in Constantinople. It served as the starting point for measurement of distances for all the roads leading to the cities of the Byzantine Empire, and had the same function as the Milliarium Aureum of Ancient Rome. The Milion survived intact until at least the late 15th century. Its fragments were discovered again in the late 1960s. A fragment is re-erected as a pillar.

In Islamic civilisation, use of milestone began in the first Islamic century. The Umayyad caliph Abd al-Malik bin Marwan laid the milestones along the paths that travelers used, and some were found in the city of Faiq in the Syrian Golan, which is, Faiq, one of the main road stations throughout the Islamic ages. The function of these stones was to guide travelers and introduce them to long distances, as the separation between one and the other was one mile. Many of these stones were found in more than one location, one in the Islamic Archeology Museum in Istanbul and another in the Jerusalem Museum. A translation of the text written on the stone currently found in the Kasserine Museum in the Golan reads as follows:

In the name of God, the Most Gracious, the Most Merciful.

There is no god but God alone, and there is no partner for it. Muhammad is the Messenger of God. He ordered the making of these miles, Abdul Malik bin Marwan, Commander of the Faithful. At the hands of a consultant, the Lord of the Faithful.

In Sha'ban from the year eighty-five, from Damascus to this stone fifty-three miles.