Mile is a length unit, which comes from ancient times. It was invented and widely used by Romans. In those times, one mile equaled 5000 Roman feet. The British road network was established by Romans, that's why the British began using miles as a length unit. Before miles a furlong (660 feet) was an important unit used by the British in agriculture, and it was important to relate miles to it. The British decided one mile to consist of eight furlongs, that's why there are 5280 feet in a mile (8 * 660 = 5280).

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