Old English mīl, based on Latin mil(l)ia, plural of mille 'thousand' (the original Roman unit of distance was mille passus 'a thousand paces').

• Where Roman legions marched they left roads, bridges, and other works of civil engineering. One thousand paces (or two thousand steps) marched by disciplined troops became a fixed and useful unit of measurement of distance—in Latin this was mille passus or mille passuum ‘one thousand paces’, later shortened to simple mille. The word entered most of the languages of Europe. When you urge someone to go the extra mile, ‘to make a special effort to achieve something’, you are echoing the Bible. In the Sermon on the Mount, in the Gospel of Matthew, Jesus says, ‘And whosoever shall compel thee to go a mile, go with him twain’ (two). See also inch, miss, million