Chapter XII: The Ancient Subterranean Aqueducts

Works of Public Utility — The System probably introduced from Persia — The Bulk of the Works carried out by the Romans — Trenches connecting Wells with Cultivable Lands — Fortress Bores and their Underground Connections — Dêr el Ghennîma — Subterranean Aqueducts of Qasr Gyb — Qasr Lebekha and Um el Dabâdib — Reopening of Tunnel by Sheikh Hassan Hanadi — Sala Abdulla — Nature of Tunnels and Shafts — The Magnitude of the Underground Works — Exploration of the Tunnels — Origin of the Water.

Although the Persians and Romans left abundant traces of their occupation of the country in the shape of temples, forts, and monasteries, the determination and energy with which they prosecuted the colonization and general development of the oases is best shown by their attention to works of public utility. At no period in the history of the oases has so much attention been paid to the water-supply. Not content with tapping the deep-seated sources by means of bores, they carried out underground works of considerable magnitude and involving engineering difficulties of no mean order, so as to obtain additional supplies from the sandstones lying at or near the surface. The methods employed were probably introduced from Persia, where underground aqueducts, or ‘kareez,’ for the transference of water from one locality to another, have from an early date been employed. At the same time, judging by the character of the ancient buildings in the immediate neighbourhood of the most important of these works, it seems probable that the latter were for the most part constructed by the Romans.

Underground aqueducts are found to some extent in all the chief oases of the Libyan Desert, but in Northern Kharga they far exceed in magnitude anything known elsewhere. In their simplest form they consist of deep trenches connecting the wells with low-lying areas of cultivable land, the object being to tap the bores at the lowest possible levels, in order to obtain the greatest discharges. Thus, although a bore, originally sunk on comparatively high ground for the purpose of irrigating a particular area of land, might through one cause or another have ceased to flow, it could still be made available for any low-lying area farther afield by the simple expedient of tapping it below the surface by means of a trench or tunnel. This practice was frequently resorted to.

In selecting sites for their forts, monasteries, and other buildings, the Romans were naturally drawn to eminences commanding views of the surrounding country. It was, of course, desirable, and in the case of forts absolutely necessary, to have a supply of water within the building, and it was the custom, therefore, to sink a deep bore within the precincts, generally in the centre of the courtyard. In many cases, however, owing to the elevation, the water would not rise to the surface, the supplies being drawn up by hand. In order to make the water of such a well available for irrigating the lands situated outside the fort, one or more gently inclined tunnels were excavated so as to tap the bore below the fort; the well was thus made to serve a double purpose. Excellent examples of such conduits are to be seen at Dêr el Ghennîma. Here the well is in the middle of the courtyard, and three underground tunnels converge on it from the low-lying and anciently cultivated lands to the north and north-west. Along those portions where the bottom of the channel was in soft ground, and not more than a metre or two below the surface, the conduit was made in the form of an open trench, the sides being carefully built in with stone.

When the excavation of the trenches was completed, the open portions were covered over with large flat slabs of rock, so that the channels were not only well protected from blowing sand, but quite invisible on the surface. The underground conduits at Dêr el Ghennîma were indeed quite unsuspected before they were accidentally discovered a year or two ago. The tapping of the bore within the fort had, of course, the effect of still further lowering the water-level as regards the courtyard; it is quite likely, therefore, that the inhabitants had a means of blocking the underground channel when they desired the water to rise to its maximum level in the well. But in any case the few extra metres of distance from the surface to the water could not have been a matter of importance, as the comparatively small supplies needed for domestic purposes within the fort were doubtless raised by means of a bucket and rope attached to a windlass.

These short tunnels, tapping the water of artesian wells bored on high ground, are quite insignificant compared with the extensive systems of subterranean aqueducts driven into the solid rock in various localities in the north of the oasis. The most remarkable of these are found at Um el Dabâdib, at Qasr Lebekha, and in the neighbourhood of Qasr Gyb. They were made with the object of obtaining auxiliary supplies of water from the Surface-water Sandstone, and were especially applicable to localities where this sandstone has an extensive development and forms hills or plateaux above the general level of the floor of the oasis. Although it is difficult to believe that the supplies of water obtained were commensurate with the time and labour involved in the construction of the collecting tunnels, we may safely assume that the engineers who so carefully planned and carried out the works had fully considered the results to be looked for. The ruins of villages and the traces of formerly cultivated tracts show that sufficient water was obtained to enable fairly large colonies to exist, though after the withdrawal of the Romans these outlying districts were abandoned, the aqueducts silted up, and the cultivated lands reverted to the desert.

The ruins of Um el Dabâdib are situated under the northern wall of the depression, and distant about 36 kilometres N.N.W. of Kharga village, the route usually followed lying between the hill-massifs of Jebel Têr and Jebel Tarif. A better route is afforded by the caravan road running from Meheriq to Ain Amûr, Um el Dabâdib lying somewhat to the north of the track at a distance of 25 kilometres from the village.

Dr. J. Ball, in the course of his survey of the oasis, visited Um el Dabâdib in 1898, and thought it possible that one of the tunnels, which he observed ran northwards from the neighbourhood of the ruins, had originally formed a means of communication with some unknown and formerly inhabited depression to the north of the escarpment. Its real nature was, however, well known to the Kharga people, and a year or two later Sheikh Hassan Hanadi, a brother of the present Omda of Kharga village, got together a number of men and cleaned out one of the tunnels from top to bottom, with the result that, after a lapse of perhaps 1,000 years, water again flowed from the mouth of the aqueduct, and enabled a small agricultural colony to establish itself on the ruined site of the original founders.

Sheikh Hassan informed me that the bulk of the work had been done under his personal supervision, by a gang of from seventy to eighty men employed throughout the hot season; he had found from experience that the natives worked better in summer than in winter. The main tunnel was entirely cleared of clay and sand, the silted material being lifted out through the numerous man-holes or vertical shafts which connect the aqueduct with the surface above. A great deal of rough masonry work had also to be undertaken where the sandstone roof or walls had fallen in. The place was put in thoroughly good order, and all the shafts again closed, with the exception of two or three left open to permit of the descent of the men sent down periodically to examine the channel and keep it free from silted material.

When I first visited the place in January, 1905, I found the discharge from the mouth of the aqueduct was between 30 and 35 gallons per minute. A dozen acres or so of land had been reclaimed, and were tended by seven or eight men, who informed me that the crops raised there were equal to those in any part of the oasis. This I can quite believe, as, in spite of the fact that several dune-belts exist in the neighbourhood, the place is comparatively sheltered from the northerly winds by the great escarpment to the north.

The little settlement of Um el Dabâdib, with its adjoining fertile fields and fruit-garden, threaded by the life-giving stream emerging from the foot-hills of the stupendous cliffs to the north, and backed by the grim fort of bygone ages to the south, has in the midst of this desert an indescribable charm.

Sala Abdulla, old Sheikh Hassan’s head-man here, proved to be a most delightful fellow, and far superior to the average native in general intelligence. He spun the most fantastic yarns about the desert tableland to the north, and—a peculiarity I appreciated most of all—without expecting me to believe him. According to Sala, traces exist of a formerly much-frequented road, said to lead to a place called Ain Hamûr, lying somewhere to the north-west of Ain Amûr. But although he himself had on one occasion set out and travelled for many hours beyond the summit of the cliffs, he had been forced to return without finding the place, the exact position of which is at the present day unknown. This out-of-the-way corner of the desert is, according to my informant, so undisturbed by man that the gazelle there live for untold periods, and only eventually succumb to old age and the increasing weight of their horns, which grow to such a size that the poor beasts are unable to move about in search of food!

On my expressing a desire to examine the underground aqueduct, Sala led the way to one of the man-holes situated a couple of kilometres to the north, near the upper end of the tunnel. Producing a palm-fibre rope from under a ledge in a cliff hard by, he attached it to a log placed across the mouth of the shaft. There was a hot, steamy current of air ascending from the man-hole, the interior of which was as black as night. Sala had, however, provided candles and matches, and when he reached the bottom and shook the rope as a signal to me to follow, I could see a tiny speck of light in what seemed to be the bowels of the earth. Fortunately I had had a good training in the Cornish and Welsh mines at home, so that the prospect of a descent by the rope did not worry me in the least, and after scrambling into the shaft I went carefully down hand over hand.

The shaft, rectangular in cross-section, and beautifully cut through the solid sandstone rock, measured roughly 1½ metres by ¾ of a metre, tapering gradually downwards. The first few metres, sunk through the down-wash forming the bed of a valley, were carefully built in with blocks of limestone, the bottom layer resting on the solid rock below. Rough footholds on opposite sides of the shaft facilitate the descent, and when nearing the bottom, as the rope stretched and contracted like elastic in a most unpleasant manner, I was glad to avail myself of their assistance. The shaft, which I afterwards found to have a depth of 40·3 metres (132 feet), goes down perpendicularly, and when the bottom was reached, I found myself standing in a gently flowing stream of water, which I knew continued its underground course for at least 2 kilometres to the south.

The tunnel itself is distinctly coffin-shaped in cross-section, being widest near the roof, and tapering downwards. Its average height is about 1½ metres, the mean width near the top being about 60 centimetres—_i.e._, it measures roughly 5 feet by 2 feet. In some places it is even narrower, so that a man of average stature not only has to keep his head very much bent, but is also forced to progress sideways if he wishes to make his way along the channel. The place was so sultry, and the cramped position I had to assume so tiring, that I had soon had enough, and groped my way back to the base of the shaft. As I had anticipated, the ascent proved considerably more difficult than the descent, and I was not sorry when I regained the surface. After the heat of the shaft and the exertion of climbing, the outside air, despite the fact that it was an exceptionally hot day, felt bitterly cold, and the rapid evaporation from our perspiring bodies chilled us to the marrow.

Although I had vowed at the time that nothing would induce me to again enter the place, I afterwards reflected that, not having followed the tunnel to its extreme limits, there might still be further information to be gained, and at the termination there might exist an inscription, the deciphering of which would yield the much-desired information as to when and by whom the work had been carried out. Moreover, I particularly wished to ascertain whether the bulk of the water came from one particular point or whether it represented the accumulated flow from the numerous small fissures which a tunnel of such length must necessarily traverse. I therefore took the first opportunity of revisiting the place, this time providing myself with proper gear to facilitate the descent, and with instruments to make a thorough survey of the whole network of underground waterways.

The accompanying sketch-map, reduced from the detailed plan made during my last visit, shows that there are four main aqueducts, running nearly parallel, in a north and south direction, along the sides of three separate valleys. It is, of course, quite evident that the tunnels were run under the valleys rather than beneath the intervening ridges with the express object of keeping as near the surface as possible, so as to avoid unnecessary excavation in the sinking of the vertical shafts, and to reduce the labour involved in hoisting the excavated material to the surface. The engineers were at the same time careful to avoid the actual beds of the valleys, as there the soft nature of the ground would have necessitated a considerable amount of stone pitching, without which there would have been constant falls of the loose detritus, consisting of sand and pebbles with large blocks of limestone, forming the actual floors of the valleys. Alignments were chosen along the extreme margins, the mouths of the man-holes being commenced on the sloping sides of the valleys, a metre or two above their pebbly floors. The great majority were thus excavated throughout in solid rock, the latter being, as a rule, sufficiently firm to stand without timbering or masonry supports.

Although only one of the four main aqueducts is open at the present time, the exact course which each follows can be seen from the dump-heaps marking the positions of the shafts. The longest of the tunnels is the most westerly, measuring 4·6 kilometres from the point of origin to its exit on the west side of the ruined fort, the four together having a total length of 14·3 kilometres. The actual length of horizontal excavation is, however, considerably in excess of this figure, as there are very numerous subsidiary collecting branches ramifying from the main tunnels. Moreover, the total length given is the figure obtained by measuring along the surface from shaft to shaft; whereas, one of the most striking things underground is the markedly irregular trend of the tunnel, which frequently takes a wide bend between two adjacent shafts.

The man-holes, or vertical shafts connecting the underground waterway with the surface, served a double purpose. Through them the excavated material was hoisted to the surface, and in addition they afforded a means of ventilation, without which it is doubtful whether the work could have been carried out. The excavation of the man-holes alone must have been a gigantic task, equal to, if not greater than, that of cutting out the horizontal tunnels. The cross-section of an average-sized shaft is, if anything, greater than that of the tunnel; and although in vertical dimension the man-holes near the mouth of the aqueduct are insignificant, the depth rapidly increases in the opposite direction, owing to the upward slope of the ground-surface towards the escarpment. As already mentioned, the particular shaft I descended had a depth of over 40 metres, and subsequent levelling, from the exit of the aqueduct to a point above its origin, showed the most northerly one to have a depth of not less than 53½ metres (175 feet). Along this tunnel, which has a total length of 2·9 kilometres, I counted exactly 150 shafts, so that their average distance apart is between 19 and 20 metres.

That the tunnel was most carefully planned and excavated is evident from its very low and gradual slope, as is indicated by the depth of water flowing through and by the generally unrippled character of the stream. Judging by the height of the mouth of one of the man-holes near the point of origin of the tunnel, and by its depth to the stream in the tunnel below, there only appears to be a fall of 1 metre in about 2½ kilometres, or a slope of 1 in 2,670. It is possible that, owing to the elasticity of the line used, there may be a slight error in the measurement of the shaft, but the above figure may be taken as approximately correct.

We have now enough data to calculate the amount of material excavated from these underground works, and this gives us a good idea of the magnitude of the task. The average depth of the man-holes (from the ground-surface to the roof of the horizontal tunnel) works out at 22 metres— that is to say, they represent a total length of vertical excavation amounting to 3·3 kilometres. Adding 10 per cent. to the length of the aqueduct, to allow for the numerous bends and the side branches, we get 3·2 kilometres of horizontal excavation, or a grand total of 6·5 kilometres. From a number of measurements the cross-section of both shafts and tunnels works out at an almost identical figure—_i.e._, three-quarters of a square metre. Thus the amount of rock excavated in this system alone is about 4,875 cubic metres, and we may safely say that the construction of the four subterranean aqueducts and the 600 or 700 vertical shafts meant the excavation and removal of over 20,000 cubic metres of solid rock.

In contemplating the time and labour involved in the excavation and removal of this great mass of material, it must not be forgotten that the latter represents the construction of underground passages over twenty miles in length, and of such restricted size that only one man could have found room to work on the face of the tunnel or shaft at a time. And although the sinking of more than one vertical shaft may have been carried on simultaneously, the cutting of the long aqueducts had almost certainly to be conducted from one side only—_i.e._, from their exits. The accumulation of water would probably have prevented the cutting out of different sections at one and the same time by separate gangs of men.

One day, in the summer of 1908, I was foolhardy enough to follow the aqueduct to its termination, from the bottom of the ninth shaft—the one I had previously descended—and in case some future visitor to Um el Dabâdib should feel inclined to examine for himself these wonderful subterranean works, it may not be out of place to give a brief account of my examination of the upper portion and termination of the aqueduct in question (the second, counting from the most westerly), so that he may benefit by my experience. My particular objects were to ascertain if the bulk of the water came from one or more large fissures, to determine whether any special characteristics marked the termination of the tunnel, and to discover whether there were inscriptions which would yield valuable information regarding the making of the aqueduct. My intention was to descend one of the uppermost shafts by means of the windlass with which, remembering my previous experience with nothing better than a very elastic native-made rope, I had been careful to provide myself. I reckoned that the distance thence to the point of origin of the aqueduct could not be so far as to entail any great difficulty or danger from insufficiency of ventilation.

Unfortunately descent by any of these shafts proved out of the question in the time available, owing to their mouths having been carefully closed by great slabs of rock, which I had no facilities for moving. This discovery upset my calculations in two ways: unless I abandoned the undertaking altogether, which I was extremely loath to do after coming so far, it would be necessary to follow the tunnel from the bottom of the ninth man-hole for at least 230 metres, and I had already experienced the difficulty of progressing even a short distance in so confined a space. Secondly, there was the question of ventilation. With an open shaft near the top there would at least have been good circulation through the greater part of the aqueduct; however, I still hoped that the upper man-holes were not so tightly closed as to render the air below entirely stagnant.

One of the natives who had taken part in the cleaning out of the aqueduct many years before asserted that the air was not altogether bad, and though I could not definitely ascertain whether or no he had been to the end of the tunnel since the closing of so many of the ventilating shafts, I determined to accept his word for it, and we descended safely to the bottom. The water felt cool by comparison with the air of the tunnel, though my thermometer showed the temperature of both air and water to be identical, registering 87° F. in both cases. It was quite sweet, though a good deal of sediment appeared when the stream was stirred up.

After making a number of measurements of the shaft and tunnel, we proceeded on our way upstream. The sides of the tunnel were everywhere beautifully cut in a light brown sandstone, the direction of the pick-marks showing that it had been excavated in the same direction as that we were following—_i.e._, from south to north. Small notches for the lights used by the workmen were plainly observable on the walls, about half-way between the floor and the roof. As a rule the tunnel maintains an elongated oval form, wider near the top than elsewhere; along one length, however, where it evidently follows a fissure, both top and bottom taper sharply, so much so that our feet constantly got jammed in the narrow, wedge-shaped channel through which the water flows. We passed many side branches, blind alleys, in fact, and the main tunnel itself zigzagged considerably, frequently turning at sharp angles, and more than once almost doubling back on itself.

The air was bad enough at the start, but seemed to get worse as we proceeded. I trusted, however, to finding a distinct improvement in the neighbourhood of the shafts, but to my dismay each one in turn proved to be hermetically sealed with masses of rock just above its junction with the tunnel, and there was not the slightest suspicion of any circulation of air, so that the only relief they afforded was the possibility of resting in an upright position. Three hundred metres, as I afterwards calculated the total distance to be, may seem little enough in the open, but to grope one’s way this distance by the light of a feeble candle along a passage so restricted that one has to proceed not only with bent head and shoulders, but half sideways, in a hot, steamy, stagnant atmosphere, is quite a different matter. My companion, being of small build and stature, was able to walk upright in comparative comfort, without continually bumping his head and bruising his shoulders, so that the want of air did not tell on him to the same extent; while I became more and more fatigued, owing to the difficulty experienced of getting sufficient oxygen from such an atmosphere in the cramped position I had of necessity to assume. On more than one occasion I sank exhausted into the water, the huge gasps of breath which I took seeming powerless to relieve the horrible sensation of stifling, and with the unpleasant prospect of getting drowned if I escaped suffocation. Yet there seemed to be ten thousand devils tempting me onwards, and although I did not know how long life could be supported under such conditions, a mad desire possessed me to see the thing through; so that whenever I was able to progress a few yards it was towards the head of the tunnel.

When eventually we reached our destination, some 15 to 20 metres beyond the last man-hole, it was only to find that the tunnel just stopped. There was no more water emerging from the rock at the end than I had seen entering at a dozen small fissures along the course we had traversed; there was no vertical excavation downwards; there were no traces of inscriptions; nothing, in fact. After all our trouble, we had drawn a blank. Although I positively dreaded the long crawl back, the very fact that every step took us towards the fresh air made me feel comparatively cheerful. After making my examination of the end of the tunnel, however, I found the space was insufficient to allow of my turning round, so that I was compelled to proceed backwards for some distance before I found room in which to turn. I must confess to never having experienced such a feeling of relief as when we eventually arrived at the bottom of the open shaft, and were able to fill our lungs with copious draughts of the air descending from above. We could see the tiny pin-hole of light far above us, and when sufficiently rested we swung the rope as a signal to be wound up. Although I got back to the surface none the worse for my adventure, with the exception of skin bruises, I would not recommend anyone to attempt the exploration of other similar tunnels unless there were open shafts on either side to insure some circulation of air.

It is now quite certain that the aqueducts derived their water from the numerous small fissures traversed, so that the yield of any single tunnel must have depended to a great extent on its total length. The general formation of the country determined the general direction of the tunnels, which, in order to keep within reasonable distance of the surface, had to follow the valleys. The latter, without exception in this district, run in a north and south direction, having formed at one time drainage-lines from the high plateau to the north. Many of the short branch tunnels are, however, driven along east and west fissures, though these could not be followed to any great distance, owing to the high ridges separating the valleys. It is also quite certain that the work of excavation was eventually stopped by the ever-increasing labour involved in the construction of the vertical shafts, the depth of which necessarily increased at a rapid rate as the surface of the ground rose when nearing the actual escarpment. For instance, in the space of only 230 metres, between the ninth and the first shafts, the depth of the man-holes increases from 40 to 54 metres, and to the north of this the increase would have been still more rapid, until the amount of vertical excavation would have become altogether disproportionate to the horizontal distance gained by the aqueduct.