the attacks of the black pirates were usually made simultaneously
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 thereafter a thousand great black