The eight-play Henriad is also known as The First Tetralogy and The Second Tetralogy; a terminology that had been in use, but was made popular by the influential Shakespearean scholar E.M.W. Tillyard in his 1944 book, "Shakespeare’s History Plays". The word "tetralogy" is derived from the performance tradition of the Dionysian Festival of ancient Athens, in which a poet was to compose a tetralogy (τετραλογία): three tragedies and one comedic satyr play. Tillyard studied these Shakespearean history plays as combined in a dramatic serial form, and analyzed how, when combined, the stories, characters, historic chronology, and themes are linked and portrayed. After Tillyard's book, these plays have often been combined in performance, and it would be a very rare occurrence for "Henry VI, part 2" or "3", for example, to be performed individually. Tillyard considered each tetralogy linked, and that the characters themselves link the stories together when they tell their own history or explain their titles.