This block is of rare artistry for its daring, unique and unified, closed composition. Depicted is a cavalry commander (hipparchos) trying to control his runaway horse. He has placed his foot firmly against a rock. On his head he wears a fox-skin cap and he is clad in exomis with full over-fold, His chlamys blows out behind him in the force of action. His face, lost at some undetermined time, is preserved in a cast. His expression is particularly determined and he has a short beard. The block differs from the others in its inventive composition, the especially realistic rendering of the anatomy of the horse with veins dilated, and the richly billowing folds of the wind-blown chlamys, all bespeaking the skillful hand of a creative master. Thus many scholars have attributed this piece to Pheidias himself. Those who see mythological representations in the frieze indentify this figure (15) as the mythical hero or king, Theseus, who introduced the «synoecism» of the scattered demes of Attica and established the Panathenaic festival. Others identify the bearded figure (15) and the bearded horseman (8) on block IV, who is of the same age and similarly clad, as the two cavalry commanders. Still others identify as Thracian allies the two above figures and figure (19) on block X, because of their Thracian garb. It is worth noting that both blocks VIII and IX were situated above the middle intercolumniation of the west end with the join between them precisely in the middle of the west frieze.