 When England changed to the shorter foot in the late 13th century, rods and furlongs remained unchanged, since property boundaries were already defined in rods and furlongs.The only thing that changed was the number of feet and yards in a rod or a furlong, and the number of square feet and square yards in an acre.The definition of the rod went from 15 old feet to new feet, or from 5 old yards to new yards.