The history of the word ‘furlong’ dates back to the Early Middle Ages. In the predominant European agricultural system of the day, known as the open-field system, the Anglo-Saxon acre was defined as a strip of land 40 rods, or 660 feet, long and four rods, or 66 feet, wide. When the land was ploughed, each furrow ran the length of the strip, such that ‘furlang’, derived from the Old English ‘furh’, meaning ‘furrow’, and ‘lang’, meaning ‘long’, came to mean ‘length of a furrow’. In Middle English, ‘furlang’ became ‘furlong’ and, in the Late Middle Ages, the term was used to describe a standard unit of length measuring 660 feet or, in other words, 220 yards or one-eighth of a mile.
Indeed, in the United Kingdom, the furlong remained an official measurement until it was excluded from commercial use, along with many other imperial units, by the Weights and Measures Act 1985. Nowadays, the furlong is used almost exclusively to specify the distances of horse races, traditionally to the nearest half furlong, or to indicate, in in-running comments, how far from the winning post a specific event, or events, took place; a typical in-running comment might include something along the lines of ‘…ridden and good headway to chase clear leader over 3f out, closing 2f out, led over 1f out…’ and so on.
By the time organised horse racing began, under the auspices of King Charles II, a.k.a. ‘Old Rowley’, in the second half of the seventeenth century, the furlong was a long-established unit of distance which, along with miles and yards, was particularly applicable on the racecourse. Certainly, for shorter races, the furlong provides a clear, unambiguous method of specifying fractions of a mile and, although not strictly necessary in modern horse racing, the tradition continues.