Units of length based on the human foot are common in the traditional units of world history.
The foot as a fraction of Edward I's yardEdit
It appears that the earliest official definition of the yard (then referred to as the ulna) was in a statute of King Edward I (1272-1307). This statute also defined its sub- and aggregated divisions, including the foot, in the following words:
"It is remembered that the Iron Ulna of our Lord the King contains three feet and no more; and the foot must contain twelve inches, measured by the correct measure of this kind of ulna; that is to say, one thirty-sixth part [of] the said ulna makes one inch, neither more nor less... It is ordained that three grains of barley, dry and round make an inch, twelve inches make a foot; three feet make an ulna; five and a half ulna makes a perch (rod); and forty perches in length and four perches in breadth make an acre."