Monsters Are Both Real and Metaphorical
To modern sensibility the fact of a story’s being allegorical makes it less likely to be an accurate depiction of real events. Modern writers try to drain their texts of meaning, to flatten them out in order to make them more naturalistic.
To the ancients, who believed that every single thing that happens on earth is guided by the motions of the stars and planets, the more a narrative brought out these ‘poetic’ patterns, the truer and more realistic the text.
So, it may be tempting to view the journeys into the Underworld made by Hercules, Theseus, and Orpheus as mere metaphor. It is true that on one level their adventures represent the beginning of humanity’s coming to terms with the reality of death. But, as we try to imagine the adventures underground of Hercules, Theseus, and the others, we must not conceive of them as to be purely internal or mental journeys, such as we might contemplate today. When they battled with monsters and demons, they were confronting forces that infested their own beings, the corrupted human flesh, the dark labyrinth of the human brain. But they were also fighting real monsters of flesh and blood.
— The Secret History of the World, p. 146