Islamic Civilization

Civil Engineering

One of the recurrent problems encountered in the reading of the history of science goes beyond the neglect of Islamic contribution, and that is the systematic taking away of such accomplishments from the Muslims as is the case here. Smith notes, indeed, how irrigation technologies found in Spain were acknowledged to be of Islamic origins until 1864, when the French historian, Aymard, in his Irrigations du Midi et de l’Espagne, denied any such Islamic role, and was followed by others, who built on his legacy to attribute such skills to post Muslim Spain.[1] This has become a generalised practice amongst Western historians in their treatment of almost every single Islamic accomplishment.  Halpern has noted how many of the once great achievements of Muslim civilisation are taken away from the Muslims one after the other.[2] The dominant practice has been for historians to complement each other in the suppression of the Islamic legacy established by earlier authorities, and this has affected literally every aspect of the sciences and civilisation. Hence, in relation to chemistry, the 18^th century historian Gibbon declared that the science of chemistry owes its origin and importance to the industry of ‘the Saracens’,  ‘They first invented and named the alembic for the purpose of distillation, analysed the  substances of the three kingdoms of nature, tried the distinction and affinities of alcalis and acids, and converted the poisonous minerals into soft and salutary medicines.’[3] Yet a century after Gibbon the originality of the Muslims in all these respects had been considerably diminished. Berthelot (and his countless followers) denied them any significant contribution in this field, ascribing rather to Western alchemists whatever advances were made in the Middle Ages.[4] Equally, the Gothic style was amply demonstrated by Christopher Wren in the 17^th century to be of ‘Saracen’ authorship, at a time, when Gothic was identified with the barbaric,[5] and yet, today, hardly any modern historian sees anything Islamic in such style. The same with regard to the Arabic numerals, once shunned,[6] regarded even as a symbol of ‘Saracen magic,’[7] then, as they became the foundation of modern civilisation, and though a gradual re-working by modern historians, these numerals are no longer called Arabic, and hardly any modern historian fails to call them Hindu, or even attribute their origins to Western sources.[8] Experimentation, and the experimental method were viewed in the Western Middle Ages as dabbling with the occult, any person who performed experiments or made astronomical observations soon incurring the suspicion that he carried on forbidden intercourse with the world of demons.[9] Gradually, again, in modern historian interpretations, experimentation becomes a purely Western creation, regardless of the evidence.[10] And the list can go on endlessly, how each modern historian, building on his predecessor, removes more traces of the Islamic role, until any Islamic role is fundamentally erased from nearly all disciplines and aspects of civilisation.

In respect to hydraulic technologies developed in Spain, taking their authorship away from the Muslims runs against historical reality. If the Muslims were not the authors of Spanish dams as most Western historians assert, the question to ask then is:

‘Where did the conquering Christians learn such skills more advanced than found anywhere else in Europe’?

Had such re-conquering Christians come from parts or regions where there existed a great expertise and established tradition in such technologies, one would accept it. But this is not the case at all. Historical evidence shows that the most advanced medieval dams in any part of the West were in Spain.[11]

Secondly, it makes no sense that Westerners formerly plunged in utmost darkness suddenly, out of nowhere, in the 12^th-13^th centuries discovered all these skills, it seems by a miracle.

Thirdly, and more importantly, as will be demonstrated in the following, hydraulic  technologies, like other civil engineering skills, were a widespread art throughout the vast land of Islam, from east to west. The Muslims devised many skills, techniques, constructions and structures at least six centuries prior to anything of similar advancement and sophistication in Western Christendom. 

Dams

Dams , according to Smith, ‘not only represent some of the most impressive achievements of engineers over the centuries, but their vital role in supplying water to towns and cities, irrigating dry lands, providing a source of power and controlling floods is more than sufficient to rank dam building amongst the most essential aspects of man’s attempt to harness, control and improve his environment.’[12]

In Muslim Spain and Sicily , dams served irrigation, thus increasing yields, and making irrigation cheaper.[13] At Dizful (Iraq ), dams operated a great noria, which supplied with water all the houses of the town.[14] One of the dams built in the year 960 over the river Kur, between Shiraz and Istakhr, supplied 300 villages with water,[15] and powered mills in Khuzistan. At the Pul-I-Bulaiti dam on the Ab-i-Gargar, the mills were installed in tunnels cut through the rock at each side of the channel, constituting one of the earliest examples of hydro-power dams.[16] In Muslim Spain, from the Ebro right round the Guadalquivir, Muslim engineers built river dams, usually to feed irrigation canals but also to meet the needs of power and water supply as well.[17]

Contrary to historians’ assertions, Hill points out, there was no decline in engineering activities, including dam construction, in Muslim times.[18] On the contrary, Hill insists, the new irrigation systems and the extension of existing ones (as described under agriculture) necessitated the construction of a large number of dams, many of which were small diversion dams, but several were large.[19] Whether in the eastern or western parts of the realm, Muslim engineers were responsible for accomplishments in the field that surpassed anything seen before.  The majority of the earliest Islamic dams were completed in Arabia  itself; and full information on their height, length, and ratios between height and length is given by Schnitter.[20] In Iraq , in the vicinity of Baghdad , a considerable number of dams were built during the Abbasid Caliphate.[21] Such large dams include three across the Tigris.[22]  Consequently, a huge area around Baghdad was successfully irrigated by five cross country canals running from the Euphrates to the Tigris, water ways large enough not only to be navigable, but also requiring in one case large masonry arch bridges to give access from one tank to the other.[23] At their heads, these canals were fed by dams or side regulators, and were, apparently, quite large structures.[24] The main artery for the irrigation of the lands to the east of the Tigris was the Great Nahrawan Canal, which left the Tigris a short distance below Tikrit and rejoined the river about a hundred miles below Baghdad.[25]  Between the river and the mountains called Jebel Hamrin, the Muslim engineers enlarged the Nahrawan canal, lengthened it, and equipped it with a second inlet fed from a dam across the Tigris near Samarra (further to the North).[26] The rivers Adheim and Dyala were dammed to provide water for a huge irrigated area, and in part supplied the city itself.[27] Such works,  Smith notes, were a manifestation of civil engineering in the grand manner.[28]

Further east, in today’s Afghanistan, three dams were completed by King Mahmoud of Ghaznah (998-1030) near his capital city, one of which named after him, was located 100 km SW of Kabul, and was remarkable for its dimensions, 32m high, and 220m long.[29]

In Muslim Spain, Smith notes, a conscious attempt was made to recreate in Valencia  or Cordova or Murcia the luxuriance of the Damascene Ghuta requiring the establishment of the same technical apparatus.[30] Dams  had to be built across rivers, primary and secondary canal systems were laid down with access to a suitable low level drain, usually the parent or some other river, and a system of sluices, regulators and flow dividers had to be constructed.[31] The size of the huerta, the regime of the river and the local topography, were all factors in determining whether to use one structure or a series.[32] It is in Cordoba , on the river Guadalquivir, where what is probably the oldest surviving Islamic dam in Spain can be found.[33] According to al-Idrisi, it was built of Qibtiyya stone and incorporated marble pillars.[34] The dam follows a zig-zag course across the river, a shape which indicates that the builders were aiming at a long crest in order to increase its overflow capacity. Remains of the dam can still be seen today, a few feet above the river bed, although in its prime, it was probably about seven or eight feet above high- water level and eight feet thick.[35]  On the Rio Segura, a very large area around Murcia was watered from just one dam located upstream from the city, but lower down the same river, where it flows across the flat plain between Orihuela and Guardamar, irrigation on a comparable scale was sustained by a network of low diversion dams.[36]

Smith focuses on the Muslim use of sophisticated land surveying methods to locate their dams in the most suitable sites, and also to lay out very complex canal systems feeding into, and out of them.[37] Hill, for his part, extols most particularly Islamic techniques in desilting sluices, gauging rivers, design and location, all aiming for the structure to last as can be seen in Valencia , Cordoba  and Murcia today.[38] The Muslim ability to gauge a river and then design the dams and canals to match, as seen on the river Turia in Spain, correspond with modern measurements showing that the eight canals dug by the Muslims have between them a total capacity slightly less than that of the river.[39] Astrolabes and trigonometric calculations also aided in the feasibility of such projects. The use of the astrolabe, for instance, made it possible to find the breadth of a river. The instructions were:

‘Stand at the bank of the river and hold the astrolabe in your right hand and look through the hole of the eye piece with one of your eyes, raise the level of the Alidade and look towards the opposite bank. Keeping the alidade in the same position, look towards the ground. Note the point thus obtained. The difference between these points will give the width of the river.’[40]

The dams erected by the Muslims prove the innovative, pioneering Islamic engineering ingenuity in the field. Many structures all over the Islamic world are witness to this. In the East, Schnitter notes that, with the exception of the Qusaybah dam near Madinah, a 30 m high-205 m long structure, which was slightly curved in plan, the alignment of all others was straight.[41] About half such dams were provided with a flood overflow at one end, and often with a downstream training wall to guide the spilled water to a safe distance from the dam’s foot. Schnitter also observes that about a third of such very early dams (7^th-8^th century) were still intact.[42] In some cases dams were built with carefully cut stone blocks, joined together by iron dowels; the holes in which the dowels fitted were filled by pouring in molten lead.[43] The result was an impressive structure of masonry such as the dam at Marib in Yemen  with its carefully cut and fitted blocks using lead dowels in their joints.[44] It was also fourteen metres high and 600 metres long, with elaborate waterworks including sluices, spillways, a settling tank and distribution tank. It was so good a structure, it survived for about ten centuries until lack of financial and technical means made it impossible to maintain.[45] One dam, in the neighbourhood of Baghdad , on the Uzaym river, was 575 feet long, with a trapezoidal cross section, 10 feet thick at the crest and 50 feet thick at the base, its maximum height being over 50 feet. It was built of cut masonry blocks throughout, connected with lead dowels poured into grooves, which is a fairly common Muslim technique.[46] In Iran  can be found the Kebar dam, dating from the 13^th century, the oldest arched dam known to have survived.[47] The dam has a core of rubble masonry set in mortar, the mortar made from lime crushed with the ash of a local desert plant, the addition of ash making the lime hydraulic. This resulted in a strong, hard and impervious mortar, ideal for dams, the very reason for the dam's long life, and the absence of cracks in it.[48]

In Spain, the first arched dam in Spain was the Almansa dam, which marked the beginning of a long tradition of the sort in that country.[49] According to Scott, the masonry of the reservoirs was of the finest description, and the cement used was harder than stone itself.[50] Contingencies were also provided so that no overflow occurred, and no damage resulted even during the worst flooding. Evidence of Muslim engineering ‘genius’ is proved by the fact that these dams needed hardly any repair in a thousand years.[51] The eight dams on the Turia River, at first sight seem to have an exaggerated amount of weight placed on their foundations, the masonry of each dam going some fifteen feet deep into the river bed, and further support provided by the addition of rows of wooden piles.[52] Such solid foundations were justified by the river’s erratic behaviour, which in times of flooding reaches a flow that is a hundred times greater than normal, the structure having to resist the battering of water, stones, rocks and trees.[53] On the River Segura, the Muslims built a dam in order to irrigate vast lands in the Murcia region. But because of the nature of the terrain, location, design and construction had to be perfected. Thus, the height of the dam was only 25 feet, yet its base thickness was 150 and 125 feet. This may seem excessive,[54] but such thickness was necessary to meet the softness and weakness of the river’s bed to prevent it from sliding along.  The water flowing over the crest initially fell vertically through a height of 13-17 feet on to a level platform, running the length of the dam. This served to dissipate the energy of the water spilling over the crest.[55] The over-flow then ran to the foot of the dam over flat or gently sloping sections of the face. In this way the whole dam acted as a spillway and the energy gained by the water in falling 25 feet was dissipated en route; thus the risk of undermining the downstream foundations was greatly reduced. As with other dams, rubble masonry and mortar were used for the interior, and the whole was finished with large masonry blocks.[56]

In the Maghrib  the most original reservoirs of all are found at Al-Qayrawan  in Tunisia . These reservoirs, due to their sophistication, were, despite all evidence,[57] attributed to both Phoenicians[58] and Romans.[59] Watson notes, how Gauckler, following the previous practice of European historians writing on the region, assigned virtually all the ruined irrigation works of Tunisia to the Romans.[60] Such erroneous views were adopted by a number of learned historians until more recent archaeological excavations and studies proved their 9^th century Islamic origin. Solignac’s article on the subject also works towards the same corrective aim.[61] Indeed, the construction of such dams goes back to the year 862, during the Aghlabid rule of the country.[62] We have here, in one part, water channels open to the sky, and in another, reservoirs meant for storing up streams of running water and, in some cases, water from certain springs and certain underground water levels.[63] These reservoirs have two basins, one for decantation, one as a reserve, and sometimes, a third for drawing water from it.[64] The two impressive linked cisterns were constructed for receiving the waters of the Wadi Merj al-Lil when it was in flood. These cisterns, which still stand, although appearing to be circular, both are actually polygonal, the larger having a diameter of just under 130 metres, the smaller one a diameter of 37.4 metres.[65] The smaller receives the waters of the wadi and acts as settling tank; a circular duct, several metres above its base connects it to the larger cistern, which has a depth of about eight metres.[66] On leaving the larger cistern, the water is decanted a second time into two oblong covered cisterns.[67] Other than their impressive numbers, such reservoirs also offer a great attraction in their form and structure.

Bridges

Diversity in landscapes and local conditions imposed a wide variety of designs and techniques in bridge construction; each bridge being constructed according to its own topographic setting.

Pontoon bridges were common, quick to assemble and highly practical.[68] Many Muslim towns such as Baghdad , Seville , Fustat, etc, spread along both sides of a river, and had to be connected by such bridges. They were common in Iraq  for crossing the two rivers and the major canals. In the 10^th century, for instance, there were two such bridges over the Tigris at Baghdad.[69] In Cairo , a pontoon bridge crossed from the city to the Island, and a second from there to the far bank of the river.[70] About two centuries later, al-Idrisi describes the same arrangements, adding that there were 30 boats in the first bridge and 60 in the second.[71] The pontoons were tied at both ends by iron chains, and attached at each bank to firmly implanted posts. The traveller Ibn Jubayr , writing at the end of the 12^th century, describes a bridge of large boats over the Euphrates at Hilla (which had chains on either side ‘like twisted rods,' which were secured to wooden anchorages on the banks), and a larger one over a canal near Baghdad.[72]  Ibn Jubayr also mentions a similar, but larger bridge over a canal near Baghdad.[73] There were also pontoon bridges on the rivers of Khuzistan,[74] and on the Helmand river in Sijistan.[75] Almost everywhere these bridges were supplemented by ferry services used to carry men, animals and goods.[76] To avoid permanently blocking the waterway, the bridges across the canals were constructed of movable planks, which were taken up at certain times of the day.[77] Erection of pontoon bridges on flowing currents, and anchoring boats at the right distances to receive the beams and decking of the roadway were challenging, though.[78] Under such conditions, very heavy cables were used, and high maintenance was required.

Bridges of boats were not common in medieval Europe, but some were built, the first Rialto bridge in Venice, for instance, was a pontoon bridge built in the 13^th century.[79]

Stone bridges were also constructed in large numbers, and were innovative in their architecture. In Susiana, for instance, a pre-Islamic Sasanid bridge arch was daring in the length of its span, and baskets and pulleys had to be used to get down into the foundations, whilst the stonework was bound together with iron and lead.[80] Many arch bridges were subsequently built in Muslim times, not only on rivers but also over irrigation canals.[81] They served not just in carrying transport over water, but also in clearing the way for boats wherever waters were navigable. These bridges were constructed early in Islam, the 10^th century geographer al-Istakhri describes one such bridge built under Umayyad rule in the late 7^th century under the governor al-Hajjaj (661-714).[82] It was a single arch of about 80 paces span, and so high that a man on a camel with a long standard in his raised hand could pass beneath it.[83] Ibn Jubayr  cites another such a bridge constructed by Ibn Tulun (9^th century ruler of Egypt ), which had forty arches, and was intended for military purposes, forming the first part of a causeway six miles long leading from the west bank of the Nile, from near the old quarter of Fustat in the direction of Alexandria.[84] It was used as a passage for troops over the Nile floods, if an enemy approached from the East.[85] Ibn Jubayr also mentions the many arch bridges over canals near Hilla in Iraq .[86]  Al-Qazwini (d. 1283) has left us a good description of the rebuilding of a great arch bridge at the town of Idhaj in Khuzistan in the 10^th century.[87] The bridge was 150 cubits in height and consisted of a single arch, supported on tapering masonry piers strengthened with lead dowels and iron clamps. The slag from iron workings was used to fill the space between the arch and the roadway.[88] Under  the Ottomans , a bridge built in the province of Thrace had 174 arches, and was 1,266 metres long.[89] Islamic excellence in the construction of arch bridges is illustrated by the survival of many of them until the present day.[90]

Suspension bridges were used to cross ravines in hilly countries. In the 10th century, Ibn Hawqal describes how the river Tab in Iran  was crossed by a wooden bridge ‘suspended between the sky and the water, its height above the water about 10 cubits.'[91] The design of early Islamic suspension bridges, and large modern steel bridges, such as the Forth railway bridge in Scotland, Hill notes, are built on exactly the same principles.[92]

The Islamic dominance in the field is noted by Hill, who observes that in non-Islamic Europe no bridges of note were built between the end of the Roman Empire and the 12^th century.[93] After a time, however, the building of masonry bridges began in earnest. One of the earliest of these was the famous bridge at Avignon (southern France), begun in 1177, parts of which stand today.[94]

Canals, Qanats, and Surveying

Canals served for irrigation, transport and urban supply of water throughout the Islamic world. In the south of Iraq , due to the influence of the tides on the Shatt al-Arab and the lower reaches of the Tigris and Euphrates, there is a particularly favourable situation for irrigation.[95] Thanks to a system of canals specially adapted to the situation, there is no need to use machines to raise the water to the fields, since it is always sufficiently raised by the tides to irrigate the fields.[96] The cleansing of the canals is done automatically by the movement of the tides, and drainage is effected during the ebb tide. There is, therefore, no danger of salinisation, despite the presence of dissolved salts in the water due to the proximity of the sea.[97] The Basra  area, in the summer months, presents an area of vast plantations of date palms, providing shade for flourishing vegetable gardens.[98]  Under Caliph Omar  (caliph 634-644), early canal construction took place there, and in the 660s, it was supplied with great canals, one of which came down from the north east and carried shipping from Baghdad , whilst the other carried ships to the Gulf.[99]

Further north, Damascus  had an extensive and complete water system, the rivers Barada, Qanawat, and Banyas supplying the city through two sets of underground canals, one for fresh water and the other for drainage, which brought water to mosques, schools, baths, public fountains, and private homes.[100] Makkah  also possessed three reservoirs, which were filled from the canals,[101] whilst in the Muslim West,  in Marrakech , water was brought to the city for drinking and irrigation by mainly subterranean canals from the mountains twenty miles to the south.[102] Casablanca, too, had long had a network of water channels, some above the ground, and some below, which take the water as far as individual houses, as well as drains crossing the various quarters.[103]

The qanat system, as seen above (under agriculture), was also widely diffused by the Muslims for both irrigation and urban water supply.[104] The word ‘qanat' in Arabic, Pacey explains, is said to be the same of the English word ‘canal' which was initially used to mean a pipe, or tunnel carrying liquid.[105] It consists, primarily, in tapping deep ground water without the use of lifting devices, but by sinking a series of wells and linking them underground.[106] The vertical shafts constructed along the line of the qanat allow access for maintenance and removal of spoil.[107]

The shortest and best outline on the construction of a qanat is provided by Crowe et al. It says:

‘The construction of a qanat makes a fascinating study. When a particular source of water is located, say at the foot of a mountain, a vertical master shaft is dug or drilled to the level of the water, which may vary considerably but does not usually exceed about 150 feet. The depth of the level of the water below ground is then gauged and the position of the outfall on a horizontal line is estimated by means of a series of horizontal alignments and drops along the surface. A line is then drawn between the master shaft and the point of outfall, and thence to the point where the water is to be used. This establishes the course of the qanat.

Following this line, a series of further vertical shafts is drilled, each at a distance of twenty or thirty yards apart along this line, to such a depth as to be in horizontal alignment with the level of water at the base of the master shaft. Finally, from the bottom of each shaft a tunnel is excavated to connect each length to the next, so as to extend from the outfall back to the source of water. Ultimately, a breakthrough is made on the last section, so that the water flows along the whole of the tunnel, discharging at the outfall. Here it is usually conducted into a channel, from which it is put to various uses. Normally, the horizontal tunnel is bored through the formation strata without support, but if the ground is exceptionally shaly or liable to subsidence, it may be necessary to line the excavation with brick, wood or tile. The tunnel is usually four to five feet in diameter.

Many qanats terminate in a tank or cistern from which water supplies for further uses may be drawn. But more commonly the water is conducted from enclosure to enclosure by straightforward gravity feed. Highly reticulated systems of waterways  are built up until every drop is drained and used up.’[108]

The Muslims refined the technique by using all known methods of mathematical calculation and engineering that had then become known to them.[109]

Qanats were widely used through the Muslim land, from the Middle East to North Africa , to the Iberian Peninsula.[110] The large city of Nishapur in Khurasan, for instance, was supplied entirely by qanats, most of which ran under the city and surfaced outside to form a river which irrigated the gardens of the area and many of the rural cantons.[111] Some qanats, however, surfaced inside the city and provided water to buildings and gardens. The city of Rayy, near modern Tehran, also obtained its water for drinking and irrigation from qanats.[112] At the other end of the Muslim world, the city of Tangiers was supplied by qanats from a great distance.[113]

Throughout the centuries, the Islamic qanat system spread widely, stretching from the Castilian Meseta (Madrid) to Morocco , then as far as Central America.[114] It can be traced today in the Algerian Sahara, and Oman.[115] Today, with the introduction of new drilling techniques some qanats have become obsolete, but many communities still rely entirely on water supplied in this way.[116] The widespread reliance on this system was primarily due to the fact that it saved considerable amounts of water from evaporation, and secured the transfer of water over considerable distances, even through arid deserts.[117]

The success of such civil engineering projects owes to large extent to the advance in related scientific literature. Al-Kharaji (11^th cent) treatise Inbat al-miyah al-khafiyya (The Extraction of Hidden Waters), for instance, deals with quantity surveying, that is, how to calculate the quantities of excavations for canals and hence derive the cost of the works in labour and in money. It, most importantly, describes instruments used by master well diggers and qanat builders, as well as methods of detecting sources of water and instructions for the excavation of underground conduits.[118] It includes some very interesting chapters: Chapter 17, for instance, deals with the manner and methods of resolving physical obstacles hampering tunnelling of the ground. Chapter 18 covers the manner of water adduction by the means of conduits. Chapter 19 has recipes for sealing joints of conduits. Chapter 23 covers instruments for the purpose of civil engineering invented by himself (al-Kharaji). Chapter 25 explains how to construct an underground qanat, whilst chapter 26 tells how to maintain the horizontality of a tunnel at both ends of the qanat. Chapter 28 deals with the management of the qanat, and chapter 30 covers the specific rules and clauses that must be included in a contract with an underground tunnel digger.[119]

There is also from Iraq  the anonymous: Kitab al-hawi li l-a'mal al-sultaniyya wa rusum al-diwaniyya (Book Comprising Public Works and Regulations for Official Accounting).[120] The lengthy second part of this work deals with levelling instruments and their use, and problems related to the construction and maintenance of canals, dykes and embankments.[121] In the work three levelling instruments are included.[122] The first is a wooden board about 70 cm long by 8 cm wide. In the centre of the board a line is drawn which meets both edges at a right angle; a plumb is fixed to this line, near one of the edges; two hooks are fixed to this edge. The second instrument consists of an equilateral triangle made of metal, with two hooks soldered to either end of its hypotenuse; a narrow hole is drilled through this side, to take the cord of a plumb line. The third instrument, called the ‘reed level,’ consists of a straight reed through which a narrow longitidunal hole is bored; in the centre, a radial hole is made into the bore.[123]

Equally revealing are Ibn al-Awwam’s observations on levelling works to be undertaken before opening up canals, and Ibn Lujun of Almeira (14^th century) studies on land levelling for the purpose of canal digging.[124] Further information on studies of Muslim techniques of land levelling can be extrapolated from Wiedemann.[125]

Muslim engineers also used triangulation techniques for the purpose of determining the heights and depths of objects, and the widths of obstacles such as large rivers by using the back of the astrolabe.[126] Al-Biruni  (d. 1050) and the Spanish Muslim, Ibn al-Saffar (d. 1035), describe the solution of various triangulation problems using the astrolabe.[127] Many other problems are also solved by similar means, and they include finding the distance between two points separated by an impassable obstruction.[128]  Al-Kharaji devotes chapter 24 of his above mentioned work to an instrument for calculating the height of a mountain; the distance from it, or the height of any visible high point from the ground, without measuring it, and provides a demonstration for this.[129]

Generally, Muslim science and practical knowledge in this subject passed intact to the Christian West, and generally via Spain. When the south of Spain was ultimately conquered by the Christians (1230s-1250s), they inherited a land highly developed in irrigation networks. Obviously they were at pains to preserve not only the works but also the framework of their operation and maintenance, thus in the edict by James the Conqueror of 1239, issued only one year after he had taken Valencia , the concluding lines of which go:

‘And so you may irrigate with them (the canals) and take waters without obligation, service or tribute; and you shall take these waters, as was established of old and was customary in the times of the Saracens.’[130]