Beyond the threat of invasion from a foreign army, untamed nature was a grave threat to Anglo-Saxon society. Nature in the poem is usually dark, cold, isolating, death-giving, and represents chaos and hell: who knows what a person will find there? Grendel emerges from this hell of nature, as the poem describes:

Grendel who haunted the moors, the wild/Marshes, and made his home in a hell./Not hell but hell on earth.

The wild moors and marshes are not places of beauty or romance, as in nineteenth century literature, but hell. Grendel symbolizes the threat of this hellish, savage nature to the mead hall. It's helpful to remember that at the time the poem was written, Europe was underpopulated, with large wilderness areas providing a real danger to humans.

The mead hall is everything nature is not: it is a place of warmth, light, safety, plenty, order, and sociality. It is the center of human society, and as such, represents all that is good. Heorot is the largest mead hall in the world and thus represents the pinnacle of civilization. In attacking it, Grendel, the representation of nature's chaos, carnage, and death, shakes the foundation of the civilized world—and expresses Anglo-Saxon society's fear of untamed nature.