"You look particularly pleased with yourself." Royan watched his face as he studied the instrument.
"Every reason to be," he told her. "Allowing one hundred and eighty feet for the height of the cliff below us, and another fifty feet for the depth of the pool, the entrance to the sink-hole is still over a hundred feet higher than your outlet through the fern grotto on the other side of the ridge."
"Which means?"
"Which means that there is a distinct possibility that the streams are one and the same. The inflow is here in Taita's pool and the outflow is from your grotto."
"How on earth did Taita do it?" she puzzled. "How did he get to the bottom of the pool? You are the engineering marvel. Tell me how you would do it." He shrugged, but she persisted. "I mean, there must be some established way of doing things like that, of working under water. How do they build the piers of a bridge, or the foundations of a dam, or - or - or how did Taita himself build the shaft below the level of the Nile to measure the flow of the river? You remember the description that he gives of his hydrograph in River God?"
"The accepted technique is to build a coffer dam " Nicholas said casually, and then broke off and stared at her. "My oath, you really are a corker. A dam! What if that old ruffian, Taita, dammed the whole flipping river!"
"Would that have been possible?"
"I am beginning to believe that with Taita anything is possible. He certainly had unlimited manpower at his disposal, and if he could build the hydrograph on the Nile at Aswan, then he understood very clearly the principles of hydrodynamics. After all, the old Egyptians' lives were completely bound up with the seasonal inundations of the river and the management of the floods. From what we have gathered about the old man, it certainly seems Possible."
"How could we prove it?"
"By finding the remains of his dam. It had to be a hell of a work to hold the Dandera river. There is a good chance that some evidence of it remains."
"Where would he have built the dam?" she asked excitedly. "Or let me put it another way, where would you site the dam if you had to do it?, "There is one natural place for it," he answered promptly. "The spot where the trail leaves the river and detours down the valley, and the river falls into the chasm.
They both turned their heads in unison and looked upstream.
"What are we waiting for?" she asked, and sprang to her feet. "Let's go look-see!
Their excitement was infectious, and Tamre giggled and danced ahead of them along the trail through the thorns and then up the valley to the point where it rejoined the river. The sun had lost the worst of its heat by the time they stood once again above the falls where the Dandera. river plunged into the mouth of the chasm, and began its last lap in the race to join the Nile.
"If Taita. had thrown a dam across here - " Nicholas made a sweep of his arms across the mouth of the gorge, he could have diverted the river down the side valley here."
"It looks possible," she laughed. Tamre giggled in sympathy, not understanding a word of what they were saying, but enjoying himself immensely.
"I would need a dumpy level to take some shots of the actual fall of the land. It can be very deceptive, but with the naked eye it does look possible, as you say." He shaded his eyes and looked up the bluffs on each side of the waterfall. They formed two craggy portals of limestone, between which the river roared as it plunged over the lip.
"I would like to climb up there to get a clearer picture of the layout of the terrain. Are you game?"
"Try and stop me,', she challenged him, and led the climb. It was a heavy scramble, and in some places the limestone was rotten and crumbling dangerously. However, when they came out on the summit of the eastern portal they were rewarded with a splendid overall view of the ground below.
Directly to the north, the escarpment rose like a sheer wall with its battlements crenellated and serrated. Above and beyond it there was a dream of further mountains, the high peaks of the Choke, blue as a heron's plumage against the clearer distant blue of the African sky. All around them were the badlands of the gorge, a vast confusion of ridges and spines and reefs of rock of fifty different hues, some ash-grey and white, others black as the hide of a bull buffalo, or red as his heart blood. The river in bush was green, the poisonous vivid green of the mamba in the treetop, while further from the water the scrub was grey and sear, and along the spines of the broken kopjes stood the stark outlines of ancient drought-struck trees, their tortured limbs twisted and black against the sky.
"The picture of devastation," Royan whispered as she looked around her,
'untamed and untaniable. No wonder Taita chose this place. It repels all intruders."
They were both silent for a while, awed by the wild grandeur of the scene, but as soon as they had recovered from the exertion of the climb their enthusiasm resurfaced.
"Now you can get a good picture of it." Nicholas pointed down into the valley below them. "There is a clear divide at the fork of the valley. You can see the natural fall of the ground. There, from that side of the gorge to that point below us, is the narrowest part. It is a neck where the river squeezes through - the natural site for a dam." He swivelled and pointed down to the left of where they sat.
'it would not take much to spill the river into the valley.
Once he had finished whatever he was up to in the chasm, it would taken even less to break down the wall of the dam and let the river resume its natural course again."
Tamre watched their faces eagerly, turning his head to each speaker in turn, uncomprehending, but aping Royan's expression like a mirror. If she nodded he nodded, when she frowned he did the same, and when she smiled he giggled happily.
"It's a big river." Royan shook her head, while Tamre wagged his from side to side in sympathy and looked wise.
"What method would he have used? An earthen dam?
Surely not?" i "The Egyptians used earthen canals and dams for a great many of their irrigation works,'Nicholas mused. "On the other hand, when they had rock available to work with ..", they used it extensively. They were expert masons. You have stood in the quarries at Aswan."
"Not much topsoil here in the gorge," she pointed out.
"But on the other hand, there is plenty of rock. It's like a geological museum. Every type of rock that you could wish for."
"I agree," he said. "Rather than an earthen wall, Taita would most probably have used a masonry and rock fill.
That is the type of dam the ancients built in Egypt, long before his time. If that is the case, there is a chance that traces of it have survived."
"Okay. Let's work on that hypothesis. Taita built a dam of rock stabs, and then he breached it again. Where would we find the remains of it?"
"We would have to start searching on the actual site," he answered.
"There at the neck of the gorge. Then we would have to search downstream from there."
They scrambled down the slope again, with Tamre picking out the easiest route for Royan, stopping to beckon her whenever she faltered or paused for breath. They came out in the neck of the valley and stood on the rocky bank of the river, looking about them.
"How high would the wall have been?" Royan asked.
"Not too high. Again, I can't give you a precise answer until I have shot the levels." He climbed a little way up the side of the wall. There he squatted and turned his head back and forth, looking first down the length of the valley and then towards the lip of the waterfall that dropped into the mouth of the chasm.
Three times he changed his position, on each occasion moving a few paces higher up the slope. The cliff became steeper the higher he climbed. In the end he was clinging precariously to the side of it, but he seemed satisfied. Then he called down to her.
"I would say this is about it, where I am now. This would be the height of the dam wall. It looks about fifteen feet high to me."
Royan was still standing on the bank, and now she turned and stared across at the far bank of the river, estimating the distance to the limestone cliff rising above it.
"Roughly a hundred feet across," she shouted up to him.
"About that," he agreed. "A lot of work, but not impossible."
"Taita. was never one to be daunted by size or difficulty." She cupped her hands around her mouth to shout up to him. "While you are up there, can you see any sign of works? Taita would have had to pin the dam wall into the cliff."
He scrambled along the cliff, keeping to the same level, until he was almost directly above the falls and could go no further. Then he slid down to where Royan and Tamre waited.
"Nothing?" she anticipated, and he shook his head.
"No, but you can't really expect that there would be anything left after nearly four thousand years. These cliffs have been exposed to wind and weather for all that time. I think our best bet will be to look for any surviving blocks from the dam wall that might have been carried away when Taita. breached it to flood the chasm again."
They started down the valley, where Royan came upon a chunk of stone that seemed to be of a different type from the surrounding country rock. It was the size of an oldfashioned cabin trunk. Although it was halfcovered by undergrowth, the uppermost end - the one that was exposed - had a definite right-angled corner to it. She called Nicholas across to her.
"Look at that." Royan patted it proudly. "What do you think of that?" He climbed down beside herand ran his hands over the exposed surface of the stab. "Possible," he repeated. "But to be certain we would have to find the chisel marks where the "old masons started the fracture. As you know, they chiselled a hole into the stone, and then wedged it open until it split."
Both of them went over the exposed surface carefully, and although Royan found an indentation that she declared was a weathered chisel mark, Nicholas gave her only four out of ten on the scale of probability.
"We are running out of time," he said, enticing her away from her find, 'and we still have a lot of ground to cover."
They searched the valley floor for half a kilometer further, and then Nicholas called it off. "Even in the heaviest flood it is unlikely that any blocks would have been carried down this far. Let's go back and -see if anything was washed over the falls into the mouth of the chasm." They returned to the bank of the Dandera and worked their way down as far as the falls. Nicholas peered over.
"It's not as deep here as it is further down," he estimated. "I would guess that it is less than a hundred feet."
"Do you think you could get down there?" she asked dubiously. Spray blew back out of the depths into their faces, and they had to shout at each other to make themselves heard over the thunder of the waters.
"Not without a rope, and some muscle men to haul me back out of there." He perched himself on the brink and focused the binoculars down into the bowl. There was a jumble of loose rock down the - small, rounded boulders, and one or two very much larger. Some of them were angular, and some with a little imagination could be called rectangular. However, their surfaces had been smoothed by the rushing waters, and were gleaming wet. All of them seemed partially submerged or obscured by spray.
"I don't think we can decide anything from up here, and to tell the truth I don't fancy going down there - not this evening anyway." Royan sat down beside him and hugged her knees to her chest. She was dispirited. "So there is nothing we can be certain about. Did Taita dam the river, or didn't he?" Quite naturally he placed his arm around her shoulders to console her, and after a moment she relaxed and leaned against him. They stared down into the chasm in silence.
At last she drew back from him gently, and stood up.
"I suppose we should start back to camp. How long will it take us?"
"At least three hours." He stood up beside her. "You are right. It will be dark before we get back, and there is no moon tonight."
"Funny how tired you feel after a disappointment," she said, and stretched.
"I could lie down and sleep right here on one of Taita's stone blocks." She broke off and stared at him. "Nicky, where did he get them?"
"Where did he get what?" He looked puzzled.
"Don't you see! We are going at it from the wrong end.
We have been trying to find out what happened to the blocks. This morning you mentioned the quarries at Aswan. Shouldn't we consider where Taita found the blocks for his dam, rather than what happened to them afterwards?"
"The quarry!" Nicholas exclaimed. "My word, you are right. The beginning, not the end. We should be looking for the quarry, not the remnants of the dam wall."
"Where do we start?"
"I hoped you were going to tell me." He laughed out loud, and immediately Tamre bubbled with sympathetic laughter. They both looked at the boy.
"I think we should start with Tamre, our faithful guide," she said, and took his hand. "Listen to me, Tamre. Listen very carefully!" Obediently he cocked his head and stared at her face, summoning all his errant concentration.
"We are looking for a place where the square stones come from." He looked mystified, so she tried again. "Long ago there were men who cut the rock from the mountains.
Somewhere near here, they left a big hole. Perhaps there are still square blocks of stone lying in the hole?"
Suddenly the boy's face cleared and split into a beatific smile. "The Jesus stone!the cried happily.
He sprang to his feet without relinquishing his grip on her hand. "I show you my Jesus stone." He dragged her after him as he bounded away down the valley.
"Wait, Tamre! she pleaded. "Not so fast." But in vain. Tamre kept up the pace and burst into an Amharic hymn as he ran. Nicholas followed at a more sedate pace, and caught up with them a quarter of a mile down the valley.
There he found Tamre on his knees, pressing his forehead against the rock wall of the valley, his eyes shut tightly as he prayed. He had dragged Royan down beside him.
"What on earth are you doing?"Nicholas demanded, as he came up.