Mile

• 1. Introduction

  ›

  The mile is a unit of length, and for centuries it has refused to mean only one thing. The Romans walked off a thousand paces and called it mille passus. The English borrowed that idea, then bent it. By 1593, under Queen Elizabeth I, a mile in England was fixed at eight furlongs, 5,280 feet, 1,760 yards. That figure spread across an empire and survives today on road signs in the United Kingdom and the United States. But the same word has named a Roman distance of roughly 1.48 kilometres, a Chinese distance of exactly 500 metres, and a Scandinavian distance of a full 10 kilometres. So how did one word come to carry so many lengths? Why does a country abandon the mile, and why do a handful of small islands keep it? And what happens when two nations measure the same mile and quietly disagree by a few millimetres?

• 2. Roman Paces

  ›

  A thousand paces, counted every other step, gave Rome its mile. The pace was measured as the left foot striking the ground 1,000 times, and each pace was defined as five Roman feet, so the Imperial Roman mile held 5,000 Roman feet. Agrippa indirectly standardised the distance in 29 BC when he established a standard Roman foot. Surveyors carried specialised tools such as the decempeda and the dioptra to lay it out. In modern terms, Agrippa's mile measured about 1,618 yards, slightly short of today's 1,760-yard international mile. In the Greek-speaking eastern Empire the mile, written mílion, equalled eight stadia of 600 Greek feet each. It carried on as a Byzantine unit, and a structure called the Milion stood near Hagia Sophia as the zero mile marker of the Byzantine Empire. From the Roman Forum, 50,000 Roman miles of stone-paved roads radiated across the Empire, and at every mile stood a shaped stone carved with a Roman numeral counting the distance back to Rome. That carved stone gave English the word milestone.

• 3. An Arcminute Of Earth

  ›

  Claudius Ptolemy, the Greco-Roman polymath of Alexandria, tried in the 2nd century to tie the mile to the planet itself. In his Almagest and Geography he defined a mile as a geographic arcminute of longitude, one sixtieth of a degree, or one part in 21,600 of the Earth's circumference. His sources came in mismatched units, stadion, Egyptian schoinos, and Persian parasang, and his estimate of the Earth's circumference was wrong. Yet his geographical mile of roughly 185 metres became the basis of the modern nautical mile, and medieval Arab and European cartographers adopted it. The Arabic mile, al-mīl, ran to 4,000 cubits, though it was never the common Arabic measure; Arabs and Persians preferred the longer parasang. Because cubits varied, its precise length is disputed, somewhere between 1.8 and 2.0 kilometres. That range sits close to one arcminute of latitude measured north to south along a meridian, the very idea that would later define the sea mile.

• 4. The English Statute

  ›

  An old English mile of the medieval and early modern centuries measured roughly 1.3 international miles, about 2.1 kilometres, and it kept shifting by time and place. The English long followed the Roman reckoning of 5,000 feet, 1,000 paces, or eight longer divisions they called the furlong, their furrow's length. Their measuring standards passed through royal hands. By the reign of Edgar in the 10th century the prototype was an arm-length iron yardstick held by the king at Winchester, with the foot set at one-third of it. Henry I was said to have made a new standard in 1101 based on his own arm. After Magna Carta in 1215, the barons directed that the king's standard measure be kept at the Exchequer. The break came with a Weights and Measures Act in 1593, under Elizabeth I. An earlier act had shortened the foot, and since the surveyor's rod was bound up in deeds and taxation under Henry VIII, shrinking the rod would have meant a tax increase. Parliament chose instead to keep the mile of eight furlongs and raise the feet per mile. The statute reads that a mile shall contain eight furlongs, every furlong forty poles, and every pole sixteen feet and a half. That arithmetic produced 5,280 feet. Even then it was not uniform; Robert Morden's 17th-century maps carried multiple scales, his Dorset map showing three miles in a ratio of 1 : 1.23 : 1.41, the local units stubbornly longer than the statute one.

• 5. A Continent Of Miles

  ›

  The Croatian mile was devised by the Jesuit Stjepan Glavač on a 1673 map, set as an arc of the equator and fixed at 11.13 kilometres exactly. Ole Rømer standardised the Danish mile in the late 17th century, making it equal to the Prussian mile and dividing it into 24,000 feet, sometimes treated as 7.5 kilometres. The Dutch mile resisted any single value; one older definition was 5,600 ells, and because the ell itself was unstandardised the mile could run anywhere from 3,280 to 4,280 metres. In the 16th century the Dutch kept three at once, small, medium, and large, and mariners preferred the common mile of 4,000 paces, reckoning 15 of them to a degree. In 1617 Willebrord Snellius measured a degree of the Earth at 28,500 Rijnlantsche Roeden, within 3.5 percent of the true value. The Irish mile stretched to 2,240 yards, about 1.27 statute miles, built on a perch of seven yards rather than the English rod of five and a half. The Scots mile ran to 1,976 imperial yards, and Robert Burns invoked its length in the first verse of his poem Tam o' Shanter. The Welsh mile reached 6.17 kilometres, made of 9,000 paces, said to have been codified under Dyfnwal the Bald and Silent and retained by Hywel the Good, then discontinued after Edward I conquered Wales in the 13th century. The Scots mile met three legal deaths, abolished by the Scottish Parliament in 1685, by the 1707 Treaty of Union, and finally by the Weights and Measures Act of 1824.

• 6. The Long Northern Mile

  ›

  Ten kilometres is what a Scandinavian means by a mile today. Before metric standardisation in the late 19th century, the region carried many regional miles, and in Sweden they were divided by province as landskapsmil, county miles. The Dala mile stretched 14,485 metres, the Ångermanland mile 11,875 metres, the Småland mile around 7 kilometres. In 1649 the Swedish government made the Uppland mile the de facto Swedish unit mile, defined as 36,000 Swedish feet, and called it the land mile or long mile. Finland, then part of Sweden, saw its peninkulma redefined to match, a definition it carried when Finland was ceded to the Russian Empire in 1809. When Norway joined Sweden in 1814, the same 36,000-foot standard arrived, but the Norwegian foot ran slightly longer, so the Norwegian unit mile reached 11.298 kilometres. Upon metrification Finland, Norway, and Sweden all redefined their mile as 10 kilometres, since each rested on the old Swedish unit mile, already close to that figure. The modern Scandinavian mile still appears in fuel-consumption figures, often given as litres per mil, though official road signs in Norway and Sweden carry only kilometres.

• 7. Two Miles, Same Word

  ›

  By 1929, navigators got a sea mile of exactly 1,852 metres, set by the First International Extraordinary Hydrographic Conference in Monaco. The nautical mile began as one minute of arc along a meridian, and because the Earth is an oblate spheroid, a minute of latitude grows by one percent from equator to pole. On the WGS84 ellipsoid that means 6,046 feet at the equator and 6,108 feet at the poles. Earlier nations differed; the United States used 6,080.2 feet in the 19th century, while the British Admiralty mile was 6,080 feet, roughly a minute of latitude in the south of the UK. A nautical mile per hour is a knot, and both are nearly universal in air and sea navigation. The radar world built its own variants. The data mile equals 6,000 feet, 1.8288 kilometres, and the radar mile is a unit of time, the span a radar pulse needs to travel out two miles and back. The radar statute mile runs 10.8 microseconds, the radar nautical mile 12.4 microseconds. The geographical mile, based on a meridian of latitude, gave the German geographische Meile of 7.4127 kilometres, which in turn underpinned the Scandinavian nautical mile.

• 8. The Last Few Millimetres

  ›

  Two parts per million separated the old standards when the international mile arrived. The 1959 international yard and pound agreement, reached by the United States, the United Kingdom, Canada, Australia, New Zealand, and the Union of South Africa, fixed the yard at exactly 0.9144 metres, giving a mile of exactly 1,609.344 metres. The agreement resolved small but measurable gaps, about 3.2 millimetres per mile; the US standard had been slightly longer and the old Imperial standards slightly shorter. The United States kept the older measure for some land-survey data and named it the US survey mile, which runs about 3.219 millimetres longer than the international mile. The gap is meaningless over short distances but can accumulate across the State Plane Coordinate Systems that stretch hundreds of miles. The US National Geodetic Survey and the National Institute of Standards and Technology announced in October 2019 their intent to retire the US survey foot and survey mile, effective the 1st of January 2023. Beyond all these standards the mile lives on in language. A country mile means a very long distance, to go the extra mile means to put in extra effort, and Glasgow once ran a tourism campaign under the slogan Glasgow's miles better.