The light of the moon changed.

The radiance of the stars changed.

Either the line of fire was finding denser fuel to consume or it was growing appreciably closer, for the flames began to grow, to leap, and to flare.
Slone strained his ears for the thud of hoofs on sand.
The time seemed endless in its futility of results, but fleeting after it had passed; and he could tell how the hours fled by the ever-recurring need to replenish the little fire he kept burning in the pass.
A broad belt of valley grew bright in the light, and behind it loomed the monuments, weird and dark, with columns of yellow and white smoke wreathing them.
Suddenly Slone's sensitive ear vibrated to a thrilling sound.

He leaned down to place his ear to the sand.

Rapid, rhythmic beat of hoofs made him leap to his feet, reaching for his lasso with right hand and a gun with his left.
Nagger lifted his head, sniffed the air, and snorted.