The purpose of this paper is to discuss and illustrate the development of shields of arms and their accessories upon the seals of English men and women from the simple devices of the later twelfth century to the complicated armorials and complete achievements of later times. The great seal of William the Norman, like that of Edward the Confessor, had two sides. On one William was shown seated in majesty as king of the English; on the other, unlike Edward, he appeared fully armed upon horseback as duke of the Normans. This equestrian representation of a knight fully equipped with the arms and armour of his time was the type of seal adopted by the greater barons in the early twelfth century. It was upon the shields borne by these horsemen that armorial charges first appear. Part I of this paper deals with this equestrian type.