This thing all things devours: Birds, beasts, trees, flowers; Gnaws iron, bites steel; Grinds hard stones to meal; Slays king, ruins town, And beats high mountain down.

These lines are posed as a riddle in J. R. R. Tolkien’s The Hobbit. In the chapter “Riddles in the Dark,” Bilbo Baggins, lost beneath the Misty Mountains after being separated from the dwarves, encounters Gollum by an underground lake. The two agree to a riddle-game: if Bilbo wins, Gollum will guide him out; if Bilbo loses, Gollum will eat him. The quoted verse is one of the riddles exchanged in this tense scene, drawing on the traditional English riddle form and imagery of inexorable natural forces.

The riddle’s answer is “time,” figured as an all-consuming power that erodes living things and the hardest materials alike. Its catalogue of actions—devouring, gnawing, grinding, slaying, ruining, beating down—compresses centuries of decay, death, and historical collapse into vivid physical verbs. The inclusion of “Slays king, ruins town” extends time’s reach from nature into human ambition and political order, suggesting that no status or monument escapes entropy. In the story, the riddle also heightens suspense: Bilbo’s survival depends on recognizing an abstract truth hidden in concrete images.