Hardly had the rumble of the falling bridge passed when Jud slipped his arm about Will's shoulders and half-led half-dragged the fainting boy around the corner of a great rock.

"Those yellin' devils shoot too straight for us to take any chances," he remarked briefly.

The same idea had come to the rest of the party, and they followed hard on the old trapper's heels. Here Professor Ditson again took the lead.

"It'll take them some time to get across that river, now the bridge is down, if they follow us," he observed with much satisfaction. "We ought to reach Machu Pichu to-day and Yuca Valley in two days more. There we'll be safe."

"What's Machu Pichu, Chief?" questioned Jud, using this title of respect for the first time; for the professor's behavior at the bridge had made an abiding impression on the old man's mind. "It was the first city that the people of the Incas built," explained Professor Ditson.

"When the Inca clan first led their followers into these mountain valleys, they were attacked by the forest-dwellers and driven back into the mountains. There they built an impregnable city called Machu Pichu. From there they spread out until they ruled half the continent. Only the forests and the wild tribes that infested them they never conquered. At the height of the Inca Empire," went on the scientist, "Machu Pichu became a sacred city inhabited mostly by the priests. After the Spanish Conquest it was lost for centuries to white men until I discovered it a few years ago."

"Where do we go from Yuca?" questioned Jud again.

"Follow the map to Eldorado," returned the Professor, striding along the path like an ostrich.

Beyond the rock, and out of sight of the caÑon, gaped the mouth of a tunnel fully three hundred yards in length. Narrow slits had been chiseled through the face of the precipice for light and air, and although cut out of the living rock with only tools of hardened bronze by the subjects or captives of forgotten Incas, it ran as straight and true as the tunnels of to-day drilled by modern machinery under the supervision of skilled engineers. Through the slits the adventurers caught glimpses of the towering peak down which they had come, but there was no sign of their pursuers. In a moment they had vanished from the naked rock-face against which they had swarmed.

Joe stared long through one of the window-slits, while below sounded the hoarse, sullen voice of the hidden river.

"I not like their going so soon," he confided at last to Jud. "Perhaps that Dawson have another secret way down the mountain, as he did at Wizard Pond."

"It's not likely," returned Professor Ditson, who had overheard him. "At any rate, the only thing to do is to press on as fast as possible."

"Why didn't my snake-skin make us safe from those people?" inquired Joe, as they hurried along.

"Because," explained the scientist, "the Miranhas are an outlaw tribe who have no religion and keep no faith. Nothing is sacred to them."

Beyond the tunnel a wide pavemented road led around the rear of the mountain and then up and up and in and out among a wilderness of peaks, plateaus, cliffs, and precipices.

In spite of the well-paved path along which in the old days the Incas had sent many an expedition down into the Amazon Valley, the progress of the party was slow. Will became rapidly weaker and for long stretches had to be helped, and even carried along the more difficult parts of the path.

Hour after hour went by. Once they stopped to eat and rest, but their tireless leader hurried them on.

"We're not safe on this side of Machu Pichu," he said.

Will pulled himself to his feet.

"I'm the one who's keeping you all back," he said weakly. "From now on I walk on my own legs!" And, in spite of the others' protests, he did so, forcing his numbed nerve-centers to act by sheer strength of will. Toward the middle of the afternoon the path turned an elbow of rock, and in front of them towered a chaos of grim and lonely peaks, spiring above caÑons and gorges which seemed to stretch down to the very bowels of the earth. In the background were range after range of snow-capped mountains, white as the clouds banked above them, while in front showed a nicked knife-edge of dark rock. The professor's face lightened as he looked.

"On that ridge," he said, stretching out his arm, "lies the Lost City!"

The path led downward until, although it was early afternoon, it became dim twilight in the depths of dark caÑons, and then, twisting like a snake, came back to the heights, skirting the edges of appalling precipices in a series of spirals. As the way reached the summit of the ridge it became narrower and narrower, and at intervals above it stood stone watch-towers on whose ramparts were arranged rows of great boulders with which the sentinels of the Incas could have swept an invading army down to destruction in a moment. The path ended at last in a flight of steps cut out of the solid rock, with a wall on each side, and so narrow that not more than two could walk up them abreast. It was past sunset when the little party reached the last step and stood on the summit of the windswept ridge. In the east the full moon was rising above the mountains and flooded the heights with light white as melting snow.

Before them stretched the city of Machu Pichu, its shadows showing in the moonlight like pools of spilled ink. Lost, lonely, deserted by men for half a thousand years, the great city had been the birth-place of the Incas, who ruled mightily an empire larger than that which Babylon or Nineveh or Egypt held in their prime. In its day it had been one of the most impregnable cities of the world. Flanked by sheer precipices, it was reached only by two narrow paths enfiladed by watch-towers, eyries, and batteries of boulders. To-night the terraces were solitary and the strange houses of stone and vast rock-built temples empty and forsaken.

In the moonlight this gray birth-place of an empire lay before the travelers from another age, silent as sleep, and, as they passed through its deserted streets, the professor told them in a half-whisper thousand-year-old legends which he had heard from Indian guides. At the far side stood the great watch-tower Sacsahuaman, guarding the other path, which spiraled its way up the slope of a sheer precipice half a mile high.

"The Inca who built that," said the professor, "gave the tower its name. It means 'Friend of the Falcon,' for the Inca boasted that the hawks would feed full on the shattered bodies of any foe who tried to climb its guarded heights."

On the summit of a sacred hill he showed them a square post carved out of the top of a huge rock whose upper surface had been smoothed and squared so that the stone pillar made a sun-dial which gave the time to the whole city. Near by lay Sayacusca, the "Tired Stone," a vast monolith weighing a thousand tons, which was being dragged to the summit by twenty thousand men when it stuck. As the carriers struggled to move its vast bulk, it suddenly turned over and crushed three hundred of them. Convinced that they had offended some of the gods, the stone was left where it fell, and the skeletons of its victims are beneath it to this day.

High above the rest of the city was the sacred Sun Rock. From it the sun itself was believed to rise, nor might it be touched by the foot of bird, beast, or man. At the height of the Inca Empire it was plated all over with gold, which the Peruvians believed fell to the earth as the tears of the sun, and with emeralds and, except during the Festival of the Sun, covered with a golden-yellow veil. To-day its glory had departed, and the tired travelers saw before them only a frayed and weather-worn mass of red sandstone.

Seated on its summit, the scientist showed them the street where, during the Festival of the Sun, the Inca would ride along a pavement made of ingots of silver on a horse whose mane was strung with pearls and whose shoes were of gold. Beyond the Sun Rock was the Snake Temple, which had three windows and whose solid stone walls were pierced with narrow holes through which the sacred snakes entered to be fed by the priests.

"We might camp there," suggested Professor Ditson. "It would make a large, comfortable house."

"No, no," objected Jud shudderingly. "No snake temple for me."

They finally compromised on Sacsahuaman, whose thick walls were slit here and there by narrow peep-holes and whose only entrance was by a narrow staircase of rock cut out of the cliff and guarded, like most of the entrance staircases, by rows of heavy boulders arranged along the ledge. Inside were long benches of solid stone, and, best of all, at the base of a white rock in the center of the tower trickled an ice-cold spring whose water ran through a little trough in the rock as it had run for a thousand years. Professor Ditson told them that in the old days it had always been kept guarded and munitioned as a fortress where the Incas could make a last stand if by any chance the rest of the city should ever fall into the hands of their enemies.

That night they kindled a fire within the tower, and ate their supper high above the sacred city on the battlements where the guards of the Incas had feasted a thousand years before Columbus discovered the New World. Afterward they slept, taking turns in guarding the two entrances to the city from the same watch-towers where other sentries had watched in the days of the beginning of the Inca Empire.

The next morning Will could not move. The stress and strain and exertion of the day before had left him too weak to throw off the numbing effect of the virus. Professor Ditson shook his head as he looked him over carefully.

"There is only one thing to do," he said at last. "We must send on ahead and get a horse or a burro for him. He has walked too much as it is. Any more such strain might leave him paralyzed for life. Hen," he went on, "you know the trail to Yuca. Take Joe and start at once. You ought to run across a band of vaqueros herding cattle long before you get to the valley. Bring the whole troop back with you. I'll pay them, well, and they can convoy us in case the Miranhas are still after us."

A few minutes later Hen and Joe were on their way. Leaning over the parapet of Sacsahuaman, the rest of the party watched them wind their way slowly down the precipice until they disappeared along the trail that stretched away through the depths of the caÑon. All the rest of that day Jud and Pinto and the professor took turns in standing guard over the two entrances to the city, and in rubbing Will's legs and giving him alternate baths of hot and cold water, the recognized treatment for stings of the maribundi wasp.

That night it was Jud's turn to guard the staircase up which the party had come. Once, just before daybreak, he thought he heard far below him the rattle and clink of rolling stones. He strained his eyes through the dark, but could see nothing, nor did he hear any further sounds. In order, however, to discourage any night prowlers, the old trapper dropped one of the round boulders that had been placed in the watch-tower for just such a purpose, and it went rolling and crashing down the path.

Daylight showed the trail stretching away below him apparently empty and untrodden since they had used it when entering the city. Tired of waiting for Professor Ditson, Jud hurried up the steep slope to the fortress, meeting the scientist on the way to relieve him. The old trapper was just congratulating Will on being well enough to stand on his feet when a shout for help brought all three with a rush to the entrance of the tower. Up the steep slope they saw Professor Ditson running like a race-horse, while behind him showed the giant figure of Dawson, followed closely by half a hundred Miranhas. In another minute Professor Ditson was among them.

"They must have hidden during the night around a bend in the path and rushed up when we changed guards," he panted. "They were swarming into the tower just as I got there."

All further talk was stopped by the same dreadful tumult of war-cries that the travelers had learned to know so well.

"Steady, boys," said Jud, instantly taking command, as a veteran of many Indian fights. "Four against fifty is big odds, but we've got a strong position. Will, you sit by the staircase an' if any one starts to come up, roll one of them fifty-pound boulders down on him, with my compliments. I'll stay back here where I can watch the whole wall an' pick off any one that tries to climb up. Professor, you an' Pinto keep back of me, with your ax an' knife handy in case any of them get past me. Now," he went on, as the three took their stations, "how about some breakfast?"

After the first fierce chorus of yells there was a sudden silence. Led by Dawson, the Indians were far too crafty to attempt a direct charge up through the narrow gateway. The roofless walls, no longer raftered by heavy timbers, as in the Inca's day, were the weak spot in the defense of the besieged. If enough of the Miranhas succeeded in scaling them in spite of Jud's markmanship, the defenders of the fort could be overpowered by sheer weight of numbers. While the little party of the besieged were eating breakfast at their several stations, they could hear the sound of heavy objects being dragged across the paved street without, and the clink and jar of stone against the wall. Always, however, the besiegers kept themselves carefully out of the range of vision from the tower's narrow loop-holes. At noon Jud insisted that Pinto cook and serve dinner as usual.

"Eat hearty, boys," the old Indian-fighter said. "You may never have another chance. I dope it out they're pilin' rocks against the walls an' when they've got 'em high enough they'll rush us."

It was the middle of the afternoon before Jud's prophecy was fulfilled. For some time there had been no sign nor sound from the besiegers. Then suddenly, from six different and widely separated points in the semicircle of stone, hideous heads suddenly showed over the edge of the wall, and, with the tiger-scream of their tribe, five picked Miranha warriors started to scramble over and leap down upon the little party below, while at the end of the curved line showed the scarred, twisted face and implacable eyes of the outlaw from the North.

It was then that the wiry little gray-bearded trapper showed the skill and coolness that had made his name famous throughout a score of tribal wars which had flickered and flared through the Far Northwest during his trapping days. Standing lithe and loose, he swung his automatic from his hip in a half-circle and fired three shots so quickly that the echo of one blended with the beginning of the next. Hard upon the last report came the pop of Pinto's deadly blow-gun. Three of the besiegers toppled over dead or wounded, and with a dreadful shout Scar Dawson clawed frantically at his shoulder where a keen thorn of death from Pinto's tube had lodged. The other two Indians scrambled down in terror, and there came a chorus of appalling screams, wails, and yells from the other side of the thick wall.

"I could have got 'em all," remarked Jud cheerfully, polishing his smoking automatic on his sleeve, "but I've only got four cartridges left an' we're likely to need 'em later. Will," he went on, "you just step over to the watch-tower there an' see if there 're any signs of Hen an' Joe. A few South American cow-boys would come in mighty handy just about now."

"If they don't come before night," stated Professor Ditson calmly, "we're gone. The Miranhas are certain to rush us as soon as it gets dark."

Even as he spoke, there came from outside a wail, swelling to a shriek like the unearthly scream of a wounded horse, yet with a note of triumph and anticipation running through it. Pinto started and shivered, while Professor Ditson's face showed grim and set.

"You'll have to get us first," he muttered.

"What do they mean by that little song?" inquired Jud coolly.

"It's the hag-cry that the women raise before they torture the prisoners," returned the other. "They think they're sure of us as soon as the sun goes down."

Will returned just in time to catch the last words.

"There's no one in sight," he said. "Couldn't we slip off ourselves down the cliff?" he went on.

"Not a chance," explained the scientist. "They'd roll boulders down on us."

"Is there any way of holding them off after dark?" went on Will, after a little pause—and had his answer in the pitying silence of the two older men.

For a moment he turned very white. Then he set his teeth and threw back his shoulders.

"I'm only a kid," he said, "but I've been in tight places before. You needn't be afraid to talk plain."

"If they get over when it's too dark to shoot straight," said Jud at last, "we 're all in."

Will looked at him unflinchingly.

"Watch the stairs," he said suddenly. "I've an idea." And the boy hurried back to the little parapet that overhung the trail that ran a thousand feet below.

Beyond and above him, the rim of the setting sun was coming nearer and nearer to the snow-capped mountains that cut the sky-line of the west. Already their white crests were gleaming crimson in the dimming light. As he went, Will fumbled in his belt and pulled out a tiny round pocket-mirror, which, with a tooth-brush, a comb, and a few other light articles, he had carried all through the trip in a rubber pocket fastened to his belt.

During these happenings, miles away, concealed by the intervening range, Hen and Joe were riding at the head of a troop of hard-bitten, hard-faced vaqueros, the cow-boys of the South, whom they had met at the end of their first day's journey. Armed with Mauser rifles, and with revolvers and knives in their belts, these riders of the pampas backed their wiry little South American horses with the same ease which their brethren of the Northern prairies showed.

The leader of the troop had turned out to be an old friend of Professor Ditson, who had been with him on an expedition years before. He readily agreed to journey with Joe and Hen over the mountains to the Lost City. The men had been rounding up half a dozen hardy, tiny burros, those diminutive donkeys which can carry their own weight of freight all day long up and down steep mountain trails. It was decided to take these along for the use of the travelers. With the obstinacy of their breed, however, there was never a time throughout the day when one or more and sometimes all of the burros were not balking at this long trip away from the ranch where food and rest were awaiting them. Accordingly, it was late in the afternoon when the party reached the range behind which was hidden Machu Pichu.

Suddenly Joe, who with Hen, mounted on spare horses, was piloting the little troop, caught sight of a flicker of light across the crest of the highest peak of the range ahead of them. At first he thought that it came from the rays of the setting sun reflected from a bit of polished quartz. Suddenly he noticed, with a sudden plunge of his heart, that the light was flickering in spaced, irregular intervals. With Will and several of the other boys of his patrol, Joe had won a merit badge for signaling in his Boy Scout troop, and his tenacious Indian mind had learned forever the Morse code. As he watched now he saw the sun-rays flash the fatal S O S. Again and again came the same flashes, carrying the same silent appeal, which he knew could come from none other than Will behind the range, heliographing with the last of the sun to the chum who had stood back of him in many a desperate pinch.

As Joe glanced at the setting sun he realized how short a time was left in which to save his friends. With an inarticulate cry, he turned to Hen, who was jogging lazily beside him, and in a few quick words told him what he had read in the sky. With a shout Hen gave the alarm to the troop behind in the rolling Spanish of the pampas, and in an instant, hobbling the burros, every man was spurring his horse desperately up the steep trail. With the very last rays of the disappearing sun the message changed, and the Indian boy sobbed in his throat as he read the words.

"Good-by, dear old Joe," flickered in the sky.

As the golden rim of the sun rolled beneath the horizon, Will strained his eyes desperately, hoping against hope to see a rescue-party appear against the trail which showed like a white thread against the mountain-side. Suddenly, in the dimming light, he saw a few black dots moving against the crest of the opposite mountain. They increased in number, and, once over the ridge, grew larger and larger until Will could plainly make out a far-away troop of riders and glimpse the rush of straining horses and the stress and hurry of grim-faced men. With a shout he leaned far out over the parapet until in the distance the drumming beat of galloping hoofs sounded loud and louder.

Ten minutes later a long line of men with rifles in their hands were hurrying up the steep path that led to Sacsahuaman.

The besieged were not the only ones who knew of their coming. Outside of the walls of the fort, the Miranha band had understood Will's shout when he first saw the distant horsemen. They too had heard the hoofbeats, which sounded louder and nearer every minute, and, although the path up the precipice could be seen only from the fort, yet from without the besiegers could hear the clink of steel against the rocks and the murmur of the voices of the climbing men. Just before the rescue-party reached the fort, Jud's quick ear caught the sound of muttered commands, the quick patter of feet, and through a loop-hole he saw a black band hurrying toward the other entrance to the city, carrying with them the bodies of their dead and wounded comrades.

Even as he looked there was a shout, and into the little fortress burst the rescue-party, headed by Hen, and Joe. In another minute they swarmed through the streets of the city; but the enemy was gone. At the foot of the other path the last of them were even then slipping into the darkening valley.

Of all the band, alive or dead, one only had been left behind. Just outside the thick wall of the fort lay a huge motionless form. As Jud and Professor Ditson approached it they recognized Scar Dawson, deserted by the men whom he had so recently led. As they came close they saw that he lay helpless. Only his staring eyes were fixed upon them with an expression of awful appeal; yet there seemed to be no wound any where on his great body. As they bent over him, Pinto pointed silently to a tiny red spot showing at the front of the outlaw's right shoulder—the mark made by one of the Indian's fatal little arrows. Jud stared sternly down at the helpless man.

"You've only got what was comin' to you," he said. "You'd have tortured every one of us to death if you could," he went on but there was an uncertain note in his voice. "He's a bad actor if ever there was one," he blustered, turning to the others. "Still, though, I'd hate to see any man die without tryin' to help him," he finished weakly.

"He deserves death if any man ever did," said Professor Ditson grimly; "yet it does not seem right to let a man die without help."

"Yes," chimed in Will, looking down at the dying man pityingly; "do save him if you can."

The professor hesitated.

"Well," he said at last, "I can and I will; but I am not at all sure that I ought."

Beckoning to one of the vaqueros, he took from his pouch a handful of the brown salt that is part of the equipment of every South American cattle-man. Reaching down, he forced open the stiffening jaws of the outlaw and pressed between them a mass of salt until Dawson's mouth was completely filled with it.

"Swallow that as fast as you can," he commanded.

Even as he spoke, the muscles of the man's great body relaxed as little by little the antidote for the urari poison began to work. Fifteen minutes later, tottering and white, but out of danger, the outlaw stood before them.

"I have saved your life," said Professor Ditson, "and I hope that you will make some better use of it than you have done. Your friends went down that way," he continued precisely, pointing to the path along which the Indians had retreated. "I would suggest that you follow them."

The outlaw stared scowlingly for a moment at the ring of armed men who stood around him. Then he turned to Professor Ditson.

"For saving my life I'll give you a tip which may save yours," he said thickly. "Don't treasure-hunt in Eldorado—it's guarded!" Without another word he disappeared down the steep trail.

"I hope I haven't made a mistake," murmured Professor Ditson to himself, as he watched Scar Dawson disappear in the distance.