"It is a village of lost souls," he answered, laughing. "This strip between the ice barrier and the mountains is considered neutral ground. Some turn off from their voluntary pilgrimage down the Iss, and, scaling the awful walls of its canyon below us, stop in the valley. Also a slave now and then escapes from the therns and makes his way hither.

"They do not attempt to recapture such, since there is no escape from this outer valley, and as a matter of fact they fear the patrolling cruisers of the First Born too much to venture from their own domains.

"The poor creatures of this outer valley are not molested by us since they have nothing that we desire, nor are they numerically strong enough to give us an interesting fight-so we too leave them alone.

"There are several villages of them, but they have increased in numbers but little in many years since they are always warring among themselves."

Now we swung a little north of west, leaving the valley of lost souls, and shortly I discerned over our starboard bow what appeared to be a black mountain rising from the desolate waste of ice. It was not high and seemed to have a flat top.

Xodar had left us to attend to some duty on the vessel, and Phaidor and I stood alone beside the rail. The girl had not once spoken since we had been brought to the deck.

"Is what he has been telling me true?" I asked her.

"In part, yes," she answered. "That about the outer valley is true, but what he says of the location of the Temple of Issus in the centre of his country is false. If it is not false-" she hesitated. "Oh it cannot be true, it cannot be true. For if it were true then for countless ages have my people gone to torture and ignominious death at the hands of their cruel enemies, instead of to the beautiful Life Eternal that we have been taught to believe Issus holds for us."

"As the lesser Barsoomians of the outer world have been lured by you to the terrible Valley Dor, so may it be that the therns themselves have been lured by the First Born to an equally horrid fate," I suggested. "It would be a stern and awful retribution, Phaidor; but a just one."

"I cannot believe it," she said.

"We shall see," I answered, and then we fell silent again for we were rapidly approaching the black mountains, which in some indefinable way seemed linked with the answer to our problem.

As we neared the dark, truncated cone the vessel's speed was diminished until we barely moved. Then we topped the crest of the mountain and below us I saw yawning the mouth of a huge circular well, the bottom of which was lost in inky blackness.

The diameter of this enormous pit was fully a thousand feet. The walls were smooth and appeared to be composed of a black, basaltic rock.

For a moment the vessel hovered motionless directly above the centre of the gaping void, then slowly she began to settle into the black chasm. Lower and lower she sank until as darkness enveloped us her lights were thrown on and in the dim halo of her own radiance the monster battleship dropped on and on down into what seemed to me must be the very bowels of Barsoom.

For quite half an hour we descended and then the shaft terminated abruptly in the dome of a mighty subterranean world. Below us rose and fell the billows of a buried sea. A phosphorescent radiance illuminated the scene. Thousands of ships dotted the bosom of the ocean. Little islands rose here and there to support the strange and colourless vegetation of this strange world.

Slowly and with majestic grace the battleship dropped until she rested on the water. Her great propellers had been drawn and housed during our descent of the shaft and in their place had been run out the smaller but more powerful water propellers. As these commenced to revolve the ship took up its journey once more, riding the new element as buoyantly and as safely as she had the air.

Phaidor and I were dumbfounded. Neither had either heard or dreamed that such a world existed beneath the surface of Barsoom.

Nearly all the vessels we saw were war craft. There were a few lighters and barges, but none of the great merchantmen such as ply the upper air between the cities of the outer world.

"Here is the harbour of the navy of the First Born," said a voice behind us, and turning we saw Xodar watching us with an amused smile on his lips.

"This sea," he continued, "is larger than Korus. It receives the waters of the lesser sea above it. To keep it from filling above a certain level we have four great pumping stations that force the oversupply back into the reservoirs far north from which the red men draw the water which irrigates their farm lands."

A new light burst on me with this explanation. The red men had always considered it a miracle that caused great columns of water to spurt from the solid rock of their reservoir sides to increase the supply of the precious liquid which is so scarce in the outer world of Mars.

Never had their learned men been able to fathom the secret of the source of this enormous volume of water. As ages passed they had simply come to accept it as a matter of course and ceased to question its origin.

We passed several islands on which were strangely shaped circular buildings, apparently roofless, and pierced midway between the ground and their tops with small, heavily barred windows. They bore the earmarks of prisons, which were further accentuated by the armed guards who squatted on low benches without, or patrolled the short beach lines.

Few of these islets contained over an acre of ground, but presently we sighted a much larger one directly ahead. This proved to be our destination, and the great ship was soon made fast against the steep shore.

Xodar signalled us to follow him and with a half-dozen officers and men we left the battleship and approached a large oval structure a couple of hundred yards from the shore.

"You shall soon see Issus," said Xodar to Phaidor. "The few prisoners we take are presented to her. Occasionally she selects slaves from among them to replenish the ranks of her handmaidens. None serves Issus above a single year," and there was a grim smile on the black's lips that lent a cruel and sinister meaning to his simple statement.

Phaidor, though loath to believe that Issus was allied to such as these, had commenced to entertain doubts and fears. She clung very closely to me, no longer the proud daughter of the Master of Life and Death upon Barsoom, but a young and frightened girl in the power of relentless enemies.

The building which we now entered was entirely roofless. In its centre was a long tank of water, set below the level of the floor like the swimming pool of a natatorium. Near one side of the pool floated an odd-looking black object. Whether it were some strange monster of these buried waters, or a queer raft, I could not at once perceive.

We were soon to know, however, for as we reached the edge of the pool directly above the thing, Xodar cried out a few words in a strange tongue. Immediately a hatch cover was raised from the surface of the object, and a black seaman sprang from the bowels of the strange craft.

Xodar addressed the seaman.

"Transmit to your officer," he said, "the commands of Dator Xodar. Say to him that Dator Xodar, with officers and men, escorting two prisoners, would be transported to the gardens of Issus beside the Golden Temple."

"Blessed be the shell of thy first ancestor, most noble Dator," replied the man. "It shall be done even as thou sayest," and raising both hands, palms backward, above his head after the manner of salute which is common to all races of Barsoom, he disappeared once more into the entrails of his ship.

A moment later an officer resplendent in the gorgeous trappings of his rank appeared on deck and welcomed Xodar to the vessel, and in the latter's wake we filed aboard and below.