Kilometre Zero
In many countries, Kilometre Zero (also written km 0) or similar terms in other languages, is a particular location (often in the nation's capital city), from which distances are traditionally measured. A similar notion also exists for individual roads (that is, all locations on the road have a number, depending on their distance from that location), and for individual cities (often the city's central post office is used for this).

The most famous such marker of which any part survives from ancient times is the Milliarium Aureum ("Golden Milestone") of the Roman Empire
Roman Empire
The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....

, believed to be the literal origin for the maxim that "all roads lead to Rome".
Argentina marks Klometre Zero with a monolith in Plaza Congreso
Congressional Plaza
Congressional Plaza is a public park facing the Argentine Congress in Buenos Aires. The plaza is part of a 3 hectare open space comprising three adjoining plazas to the east of the Congress building...

 in Buenos Aires
Buenos Aires
Buenos Aires is the capital and largest city of Argentina, and the second-largest metropolitan area in South America, after São Paulo. It is located on the western shore of the estuary of the Río de la Plata, on the southeastern coast of the South American continent...