milia passuum

Milia passuum is Latin for 'a thousand paces.' A passus was a double-step: the distance from the point where one foot leaves the ground to the point where it touches down again after the other foot has stepped. A Roman passus measured about five feet, or 1.48 metres. A thousand of these double-steps covered approximately 4,854 feet — the Roman mile. The word milia (thousands) was shortened to 'mile' as it passed through Old English.

Roman roads were marked with milestones — miliaria — at intervals of one thousand paces from Rome. The golden milestone, the Milliarium Aureum, stood in the Roman Forum. Augustus erected it around 20 BCE. All distances in the Roman Empire were measured from this point. The phrase 'all roads lead to Rome' was literally true in the measurement system: every road had mileposts counting from the Forum.

After Rome fell, every country in Europe adjusted the mile to suit local needs. The Italian mile was different from the German mile, which was different from the English mile. The English statute mile was fixed at 5,280 feet by an act of Parliament in 1593, under Elizabeth I. The number 5,280 was chosen because it divided evenly into furlongs: eight furlongs of 660 feet each. The Roman thousand-pace mile and the English statute mile are related by name but not by distance.

The mile survives in only three countries as an official road unit: the United States, the United Kingdom, and Myanmar. The rest of the world uses kilometres. But the word mile persists in metaphors and idioms in every English dialect — 'a country mile,' 'go the extra mile,' 'miss by a mile.' The Latin count of a thousand paces became an English word for any long distance.