This early Poe story-- in some ways a precursor to the better known "The Black Cat"-- is subtitled "A Tale in Imitation of the German," and thus owes some of its elements to the then-current vogue for Germany's stories of horror and Gothicism.
The title is the name of one of two feuding Hungarian royal families. Frederick, the decadent young lord of the Metzgerstein family apparently sets fire to the stables of the rival family, killing many of the horses. To be sure, the reader does not see Frederick do the deed. But after it happens, a mysterious horse, claimed by neither family, shows up on Metzgerstein property. Frederick becomes obsessed with the horse, and commences to ride it. Eventually the horse carries his evil master into a blazing fire, killing him, and onlookers witness the sight of a horse-like apparition in the sky.
The apparition, being seen by people who have no particular reason to think of the horse as some avenging demon, puts the story into the domain of the marvelous.