The unit was first used in the ninth century at the latest. The word "furlong" comes from Old English words "furh" ("furrow") and "lang" ("long"). Originally it was the length of the furrow in one acre of a ploughed field. An acre is an area that is one furlong long and one chain wide. For this reason, the furlong was once also called an "acre's length". Around the year 1300, England standardized the furlong as 40 rods or 660 feet.