Why was John Fisher executed?

St. John Fisher was martyred (beheaded) on June 22,1535 on Tower Hill, Tyburn, England. He met death with a calm dignified courage which profoundly impressed all who were present. His body was treated with particular rancour, apparently on Henry's orders, being stripped and left on the scaffold till evening, when it was taken on pikes and thrown naked into a rough grave in the churchyard of All Hallow.