Doom

Passage from text:
"They looked back. Dark yawned the archway of the Gates under the mountain-shadow. Faint and far beneath the earth rolled the slow drumbeats: doom. A thin black smoke trailed out. Nothing else was to be seen; the dale all around was empty. Doom. Grief at last wholly overcame them, and they wept long: some standing and silent, some cast upon the ground. Doom, doom. The drum-beats faded."

Pg#: 323

Commentary: [Rhetorical Device]
I don't think that it's a coincidence that the drum-beat and "doom" are held synonymous in onomatopoeia. Since a chapter ago that "doom" sound has been closing in. Now in the wake of Gandalf's alleged death "doom" has truly set in. How will the company continue on? Will there be more Orcs and Balrogs where that came from? The gang had been leaning so much upon Gandalf as their guide and leader- now only sorrow and an impending sense of "doom" fills that place. The group must forge on if they are to be rid of the ring and those drum-beats.