Don Quixote's Sheep.
Don Quixote's mistaking two flocks of sheep for two armies is not without parallel. In Ariosto's Orlando Furioso, written 1516, the hero, in his madness, falls foul of a flock of sheep.
Still more ancient is "Ajax Mad," a tragedy founded on the madness of Ajax, because of the armor of Hector being awarded to Ulysses instead of himself. In his insanity, Ajax fell upon a flock of sheep, driven at night into the camp, supposing it to be an army led by Ulysses and the sons of Atreus. On discovering his mistake he stabs himself.