along the entire ribbon-like domain of the therns, which circles the Valley Dor on the outer slopes of the Mountains of Otz.
As the fighting receded from our position for a moment, Thuvia turned toward me with a question.
"Do you understand, now, O Prince," she said, "why a million warriors guard the domains of the Holy Therns by day and by night?
"The scene you are witnessing now is but a repetition of what I have seen enacted a score of times during the fifteen years I have been a prisoner here. From time immemorial the black pirates of Barsoom have preyed upon the Holy Therns.
"Yet they never carry their expeditions to a point, as one might readily believe it was in their power to do, where the extermination of the race of therns is threatened. It is as though they but utilized the race as playthings, with which they satisfy their ferocious lust for fighting; and from whom they collect toll in arms and ammunition and in prisoners."
"Why don't they jump in and destroy these fliers?" I asked. "That would soon put a stop to the attacks, or at least the blacks would scarce be so bold. Why, see how perfectly unguarded they leave their craft, as though they were lying safe in their own hangars at home."
"The therns do not dare. They tried it once, ages ago, but the next night and for a whole moon
