The Wealth of Nations by Part 1 Chapter 11 Page 107

without a licence when the price was so low as six shillings and eightpence; and in 1463 it was enacted that no wheat should be imported if the price was not above six shillings and eightpence the quarter. The legislature had imagined that when the price was so low there could be no inconveniency in exportation, but that when it rose higher it became prudent to allow importation.

Six shillings and eightpence, therefore, containing about the same quantity of silver as thirteen shillings and fourpence of our present money (one third part less than the same nominal sum contained in the time of Edward III), had in those times been considered as what is called the moderate and reasonable price of wheat.

In 1554, by the 1st and 2nd of Philip and Mary; and in 1558, by the 1st of