In Caverns Below by Stanton A. Coblentz — Read

In the first dismal moment of my imprisonment, I had anticipated days, weeks, or even months of confinement. But I might have spared my fears. I was soon to be released -- although under the last conditions I would have chosen. And the period of my incarceration, though brief in duration, was to be savage in the torments it inflicted.

Two or three hours after I had been jailed, the prison door was shoved violently inward to admit such a ferocious-looking gang of invaders that my cell-mates all murmured in fright and huddled together at the extreme end of the room. I too gave a little gasp of alarm, then tried hard to make myself inconspicuous in a dark corner under the low-hanging ceiling. In astonishment only exceeded by my apprehension, I saw a troop of ten beings, who had evidently made every effort to appear inhuman. The head of each was enveloped in a triangular mask of steel which came to a hatchet-like point in front and displayed hideous gaping apertures for the eyes, mouth, and nostrils; their bodies were encased in dark cloth covered with thin flakes of steel which clattered as they walked; their feet, which carried long spike-like spurs both in front and behind, were clothed in iron-plated boots that ran almost to the knees; their right hands bore shining weapons, shaped a little like sawed-off shotguns, the ends of which scintillated with flying sparks.