From The Black Abbot of Puthuum, published 1936:

"To add to their distress, the terrain grew rougher and steeper, and they climbed acclivitous hillsides and went down endlessly into drear valleys. Anon they came to a flat, open, pebbly space. There, all at once, it seemed that the pandemonium of evil noises drew back on every hand, receding and fading into faint, dubious whispers that died at a vast remove. Simultaneously, the circling night thinned out, and a few stars shone in the welkin, and the sharp-spined hills of the desert loomed starkly against a vermilion afterglow. The travelers paused and peered wonderingly at one another in a gloom that was no more than that of natural twilight.

'What new devilry is this?' asked Cushara, hardly daring to believe that the hellish leaguers had vanished."

Sound familiar? Not only is Borimir's line "What is this new devilry?" a rearrangement of Cushara's line, but the retreat of the horde mirrors the retreat of the "hellish leaguers" in Smith's story.

On the other hand, that's one heck of an obscure pop culture reference.