Category Water Engineering in Ancient Civilizations. 5,000 Years of History

The hydraulican-monks: Benedictines and Cistercians

We have seen that the earliest Benedictine monasteries at the end of the 8th century already were employing a range of hydraulic techniques to support their activity. Much later, in the 12th century, Saint Bernard founds the abbey of Citeaux in Bourgogne, and with it the order of the Cistercians. Throughout Europe (France, Germany, Holland, Portugal) the Cistercian abbeys are established near watercourses. But after several years of growth, these abbeys typically found it necessary to augment their water sup­plies through capturing other rivers or torrents.

The Obazine (Aubazine) abbey was founded in Limousin in 1130 by the hermit Eti­enne. This abbey quickly entered the fold of the Cistercian order. Here one can identi­fy the trace of the “canal of the monks” dating from around 1150. It is 1.6 km long aque­duct built in truly acrobatic fashion, sometimes laid along a cliff on cantilevered arches, sometimes crossing rocky outcrops. This little canal is only 1.2 m deep and 0.6 m wide; its slope is relatively flat along most of its length (5 m/km), but it ends in a virtual water­fall, descending some 60 m in its last stretch of 230 m. Several centuries later, the inge­nuity reflected in this canal is attributed to miracles performed by its founder:

“It should be further noted that the great Saint Etienne had an aqueduct built to bring water into the abbey, so that all normal needs of hygiene and cleanliness could be satis­fied. There has never been seen in France a better built or more expensive canal. It passes through inaccessible places where the Saint broke through the rocks, to the admiration of all those who see it, and, according to legend, we learn that one of these rocks, not having yield­ed after long and expensive efforts, finally crumbled of its own accord after prayers and the worthiness of the Saint to receive this flow of water.’,z, u

Citeaux is the initial site of the Cistercians, and at the end of the 12th century it was a very rich abbey. But the Vouge River on which it was situated did not have a suffi­ciently ample and regular flow to support the growing population of monks. The abbots covet the water of a gushing torrent called Cent-Fonts, some ten kilometers to the north of the abbey, which powers numerous mills belonging to several local lords. The abbots begin by obtaining a piece of land from one of these lords to build their own mill, between 1175 and 1180. Little by little, in exchange for salvation of the lords’ souls, they obtain significant land holdings for their scheme as well as shares in the mills that use the water of this torrent. Adding to their holdings through outright purchases, the abbots eventually own all of the mills. From the Duke of Bourgogne and the Bishop of Langres, the most important personages of the region, they obtain all the authorizations necessary for their project of capturing the Cent-Fonts, in return for which they agree to build and maintain bridges across the canal for the use of the peasants of Noiron, a vil­lage on the projected course of the canal (Figure 9.10).

The canal itself is finally built around 1212. Some ten kilometers long and 2 m wide, it crosses the Varaude River, a tributary of the Cent-Fonts, on a 12-meter long canal-bridge (Figure 9.11). Its slope varies from 1.9 to 5.9 m/km, and it probably cap­tures all of the water of the Cent-Fonts (around 320 l/s). Indeed, the mills located between the canal intake and the confluence of the Varaude are left without any water and thus are abandoned. The monks develop the land that they have acquired, draining the fields crossed by the canal by digging ditches and creating ponds.[479]

What did the monasteries do with all this water? In general terms the water was des­tined for two uses: pure water for human consumption, and abundant and fast-flowing water for hygiene and useful work. Captured source water is decanted in reservoirs, sometimes filtered, and then delivered to kitchens, bathrooms, laundries, and to the apartments of the abbot and his guests. In the monasteries of the order of Chartreux, whose rules require total isolation, each cell has its own supply of water and means of wastewater disposal. The supply pipes are made of clay or lead and even sometimes of wood. Water from a river powers the mills of the abbey, including at least one wheat mill and one fuller’s mill, and often several other multiple-purpose mills. Water circu­lates through the drains and keeps them clean, passes through latrines (the latrine of Royaumont being the most remarkable), and supplies the fish pond. Fish raising is very important, for the monks are forbidden to eat meat by the rules of Saint Benoit. This importance is emphasized by the large size of the fish pond of Obazine, which is 33 m long, 14.5 m wide, and 3 m deep.

The use of wind energy (over and above the powering of sailboats) had begun on the Persian-Afghan plateau in the 7th century. It then spread to China from the 12th centu­ry as we have seen in the preceding chapter. At the beginning of this century, windmills began to see rapid development in Europe as well. Did the idea come from the Crusades, or perhaps from Sicily or Spain? Or did it arise, as we have proposed for tidal mills, quite independently? After two centuries of Muslim occupation, Sicily became Normand from 1061. The geographer al-Idrissi, residing in the court of the Normand king Roger II, gives us a hint of the Sicilian use of the horizontal-wheel Persian mill: “One can find there (in the Sicilian village of Calatubo) a quarry where stones are cut for both water mills and mills called “Persian”.”[474]

Therefore it seems possible that the idea of using wind instead of water came from the Orient. But the medieval European concept of a windmill, with blades in a vertical plane, is quite different from that of the Persian mill.

First of all, in Europe these were post mills. The mechanism of a post mill sits in a wooden enclosure. The mill’s four blades are constituted of cloth stretched on a light­weight wooden frame to which the sails are tied, apparently in nautical fashion. At night the cloth sails are removed and folded. The entire assembly, including both the sails and the machinery within the enclosure, can be rotated around a sturdy oak pivot solidly anchored or lashed to the ground, thus making it possible to orient the sail into the wind. A long beam protrudes from the rear of the enclosure, like a tail or lever, to facilitate rotation of the mill. It is said that in Lincolnshire, a horse harnessed to this beam got entangled in the straps and dragged the mill around two full turns before the frantic ani­mal could be calmed down.[475]

This concept had its roots either in the flatlands of Flanders or in England. The known points of reference in Flanders are from 1114 (the Hofland mill) and 1127 (North mill). Those in England are from 1137, when a text mentions the gift of a windmill to the abbey ofReading; then in 1155, Sussex. Four other references to mills between 1180

and 1190 are from Flanders, at the mouth of the Somme River, and here are some twen­ty other references from England. This type of mill then spreads rapidly to other regions, since evidence exists from Germany in 1222, from Denmark in 1259, and from Holland in 1274. Some 120 windmills are known to have existed in the Ypres region in the 13th century. Others are found in Russia and at Venice in the 14th century.[476]

A second type of mill with its blades in a vertical plane appears in the Mediterranean area in the 13th century. In this region it was probably very difficult to find the kind of

Figure 9.9 Remains of a tower mill on a hilltop in the northern extremity of Corsica. In this particular case, the unit cannot be turned into the wind (photo by the author).

Figure 9.9 bis Ancient windmills in Crete, on the Lassithi plateau (photo by the author).

massive wood necessary for fabrication of a pivot. Thus was born the tower mill, in which the mechanism and the millstones are inside a round masonry tower. Only the conical roof of the tower, through which the horizontal axle extends, rotates to orient the sail into the wind. The sail itself also evolves to become more rigid in this kind of mill. Before long, and especially in Mediterranean regions, the technique of a sail stretched over a wooden frame, as for the pivoting mill, begins to disappear. Now each sail is of triangular shape like the lateen sails of Mediterranean sailboats, and is rigged on one spoke of a wheel as it would be on the mast of a ship. The sail is shaped by being sheet­ed to the neighboring spoke. This new concept for a mill apparently first appears in France or in Portugal in the middle of the 13th century; it then spreads toward the east­ern Mediterranean basin during the 14th and 15th centuries.[477] A tower mill dating from 1220 can be seen in Normandy (the Moulin de Pierre of Hauville).[478]

The notion of using tidal energy certainly came naturally to the people on the Atlantic coast, already familiar with both the tide and river mills. The appearances of tidal mills at several different locations would appear to have been essentially independent. We have already mentioned the Bassora mill, in Iraq, built in the 10th century. According to Frances and Joseph Gies there may be some evidence of such a mill in Ireland around the 8th century.[472] But the real development of such mills did not begin until the 12th century, more or less simultaneously at several locations in western Europe: at Bayonne (1120-1125) and in the Basque country; at Wooton in Hampshire (1132); then along all the east coast of England; at La Rochelle where there are the remains of a gift of Alienor of Aquitaine to the Templars (1139); in Suffolk and near London (1170-1180); in the

land of Guerande (1182); in Brittany at Saint-Coulomb in Ille-et-Vilaine (1181) and at Pencastel in the Gulf of Morbihan (1186); in Normandy at Dieppe (1207) and then Carentan (1277); at Zuicksee in Holland (1220); on the Tagus at Alcantara (1313); at Rupelmonde on the Escaut (1388);[473] and so forth. Mills continue to appear up until the 18th century, becoming particularly common along all the coasts of the British Isles, as well as in Brittany, where some hundred could be found (25 in the gulf of Morbihan, 15 on the Rance). All of the mills in Spain and Portugal had horizontal wheels (a vestige of their Arab heritage); those in England had vertical wheels; and those in Brittany and along the Gulf of Gascogny were both of horizontal and vertical design (but the latter enclosed). These installations most often had a single basin formed by a closure dike into which were installed the headrace, the gate, and the millwheel below it, outside the basin. The mills could begin to operate about three hours after high tide when the dif­ference in water levels between the basin and the sea became sufficiently large. The mills then ran for about six hours, until just after the hour of low tide. This daily operat­ing period could be extended if it was possible to divert the flow of a small river into the basin. But the Middle Ages did not see the development of bidirectional tidal mills; there was no operation during rising tide.

The conquest of the waterways: inland water transport and mills

The great technological phenomenon of the Middle Ages is the development of mills, perhaps a natural companion of the revival of interest in watercourses. Since the road network was in bad shape and the countryside was not safe, the development of com­merce in the 10th century first relies on the watercourses. Demographic expansion and the nearly exclusive use of cereals to feed the population drive major development of the flour trade. In this period the consumption of bread made from flour develops while consumption of porridge decreases. It was quite natural to build mills along watercours­es that were already indispensable for water supply and transport, a heritage from the Roman era. The development of mills is nothing less than extraordinary in all the regions of France, England, and Holland. On the Roussillon canal, mills are already numerous at the end of the 9th century, and 10th century mills with multiple wheels can be found on there.[465]

Twenty years after the Battle of Hastings, in 1086, William the Conqueror put together an inventory of the possessions of his English domains in the “Domesday Book”. No less than 5,624 water mills are listed here (but no windmills and only one

tidal mill). This amounts to about one mill for every fifty houses, whereas there had only been a total of about a hundred mills a century earlier. At this period all these mills were for grinding wheat. In other regions, such as Picardy, the use of mills grows rapidly – but one must not take all of the data at face value.[466] Boat-mounted mills can also be found under the Grand Pont of Paris.

In the 10th century mills are for the most part the property of lay lords or bishops. This is the “banal” mill, to which vassals, or feudal subjects, are required to bring their grain to be ground and pay an unpopular tax (the “ban”). But the use of hydraulic ener­gy goes beyond the grinding of cereals. Industrial uses appear very early on as in Andalusia.[467] The fuller’s mill uses a system of cams to beat cloth; it appears in Italy in the 10th century, and in Burgundy (France) in the 12th century. About the same time the use of hydraulic energy to power forgehammers appears using the same principle. The first hydraulic sawmill in the Christian West appears to have been in Normandy (France) in 1204, and further evidence is found here and there in later years. Hydraulic energy has many other such uses: powering bellows for hammer forges, twisting fibers in yarn works, mixing beer, etc.

Horizontal-wheel mills are found in regions under Andalusian influence, for exam­ple along the Garonne River in France. Elsewhere the mills are almost always of verti­cal-wheel design. In the 10th century they are “undershot”, driven from below like the Roman mill described by Vitruvius (Figure 6.21). The overshot wheel is driven from above and can provide more power; it appears in the 11th century in mountain monas­teries, where it is relatively easy to direct falling water to the device.[468]

The cities that begin to develop in the second half of the 11th century in western Europe establish widespread hydrographic networks, branching out from urban centers on the watercourses. Diverse water-dependent activities such as the flour, tanning, and cloth trades[469] develop along these watercourses. Populations are not very dense, and the running water contributes to the healthy environment of these newly emerging cities.

Ownership of the water mills progressively passes to the large abbeys from the 12th century on – the abbeys clearly wanted to take over both the lands and their associated water resources. Further on we describe an example regarding the very rich abbey of Citeaux in Burgundy (Figure 9.11). These ambitions of the abbeys obviously can lead to conflicts, especially when the flatness of the river slope limits the number of mills that can be supported on a given watercourse.

On the Somme river, examination of monastic archives reveals that to the west of Ham there was quite a concentration of mills (Figure 9.4) – no less than eight along some ten kilometers, and most of these mills had more than one wheel. In 1160 the monks of Bonneuil, the important parsonage of Premontre responsible for managing the abbey’s resources in this region, raised the height of the dam of the Eppeville mill (acquired before 1138) to increase its capacity. In so doing, they affected the operation of other mills in Ham, a city located several kilometers further upstream. The trial that followed lasted no less than four years, from 1167 to 1171, and involved jurists as well as lay and religious experts. The case was eventually heard in the court of Pope Alexander III. In the end the monks of Premontre were required to demolish their structure.

We can see that the development of mills necessarily included the transformation of natural rivers into managed watercourses, including overflow weirs to generate the head necessary to power the mills. The mills were sometimes co-located with the dam itself, or sometimes were placed on derivation canals, or races, issuing from the pool upstream of the dam. These races could attain lengths of several kilometers (Figure 9.5). During low-flow periods these installations kept the water level relatively high, thus favoring

the development of inland water transport.

The earliest navigation canals may have been in the 11th century, but it is not until the 15th century that locks appear in the West. Prior to this, barges had to be hauled up and down ramps. This inconvenience, along with the improvement of the road network, rapidly reduced inland water transport to a rather modest role in the overall interior com­mercial activity in Europe. Ferryboats are put into service for river crossings, and where the overbank area (submerged during floods) is much wider than the main channel (in which year-round navigation is possible), transverse levees must be built on the over­bank to bring the road to the ferry landing and thus make it possible to cross the river in all seasons[470]. Apparently these transverse levees are of little consequence to the flow of water during floods. They cause the upstream water-surface elevation to be higher, but they attenuate the severity of the flood downstream creating a kind of intermediate storage area.

Up until this time mills had only been built on small or modest rivers. But from the start of the 12th century, the know-how for such installations on large rivers began to cross the Pyrenees. At Toulouse a 400-m long dam was built on the Garonne River. This dam was set at an angle to the river to increase the effective overflow length, a technique that we saw earlier on Andalusian dams. The dam was built of two rows of wooden piles anchored in the riverbed, with rock fill dumped between the two rows to form the struc­ture. Along with two other smaller dams, this installation provided the necessary head to power a total of 45 mills, probably a record for this period (the reader may recall the dams built by the Arabs in the Fars, also designed to provide water for a number of mills

– Figure 7.4).[471] This dam, whose height is unknown, is mentioned in a text from 1177. To our knowledge, there are no other large structures like this built prior to the 15th cen­tury.

The death throes of the aqueducts and the end of the Roman way of life

With the fall of the Roman Empire, the Romano-Hellenistic urban lifestyle in the West begins to retreat rapidly. The roots of this lifestyle are found in the Cretan cities of the Bronze Age. The forums where citizens met to discuss the business of the city are among the victims of the inward-turning that characterized this troubled period. The thermal baths where water so freely flowed disappear; the beautiful public fountains dry up. The cities degrade; new urban streets are unpaved and have neither sewers nor water pipes. Water is no longer delivered, it must be drawn from wells or from the river. This is likely why Lyon, for example, moves down from the heights of Fourviere to the banks of the Saone.

The aqueducts fall into ruin one by one between the 4th and 6th centuries AD, due as much to neglect as to the deliberate action of invaders. And yet these symbols of Roman civilization remain marks of prestige for the powerful ecclesiastics who, one way or anoth­er, manage to restore them sufficiently to supply their palaces in the 8th or 9th century. These personages include Aldric, the bishop of Le Mans; Dieudonne the abbot of Saint- Germain d’Auxerre; Rigobert, the archbishop of Reims; and Didier, the bishop of Cahors. Charlemagne himself has the aqueduct of Aix-la-Chapelle1 restored. In Rome proper, the popes restore several aqueducts to service in the 7th and 8th centuries, to provide water for the mills that they build on the Janicule and for the baptismal fonts of churches.[460] [461] But the people, for their own water needs, must go directly to the Tiber, or dig wells.

It is difficult to determine the number of water mills in use at the end of the Roman Empire. But it is evident that in the 8th and 9th centuries the water mill was widely used in Carolingian agricultural domains in Switzerland and in the northern half of France, whether these domains be lay (the villas) or monastic.[462] The Benedictine abbeys that spring up in this period follow the rule of Saint Benoit which dictates that the monaster­ies be provided with water and a mill:

“(the monastery should be) set up so that everything that is needed can be found there: water,

a mill, a garden and shops so that one can practice diverse trades within the enclosure.”[463]

Where they exist, these water supply systems are nothing more than modest aque­ducts of wood (as at the Swiss monastery of Sant-Gall) or derivations from small rivers (as at the monastery of Fulda in Germany). The importance of these early monasteries to the conservation of hydraulic techniques and the approach to the medieval revival is subject to debate.[464]

In the 9th century, the Viking invaders from the north travel up the rivers and man­age to plunge western Europe into obscurity – it is even forgotten that the earth is round.

With the end of widespread famines and the development of commerce in northern and western Europe, the revival begins in the 10th century, inaugurating a long period of economic and demographic expansion. This expansion will last up until the Hundred Years’ War (1337 – 1453) and the great plague of 1348 – 1349. In the 12th century the monasteries rediscover and reproduce certain ancient authors such as Aristotle and Gallien, from Arab translations brought back from the crusades. These Arab documents are brought from al-Andalus or from Sicily where the Norman kingdom founded in 1061 welcomes Arab and Jewish intellectuals.

From the time of the first emperor there was a need for warships in support of military campaigns in the basins of the Yangtze and the Xi (near Canton). These fortified, and sometimes armored, ships were initially powered through oars manned by soldiers. But the specific needs of riverborne military operations led to a very curious invention. It was in 784, under the Tang, that a prince named Li Gao developed warships powered by paddlewheels.[456] This invention may well have come from the 5th century.

This type of boat sees major development on the Yangtze, pushed by a great naval architect named Gao Xuan, at the beginning of the 12th century when the Song retreat into south China. Paddlewheels are mounted on the sides of the vessel; the number of them is variable, but could be as many as eleven on each side, often with a large wheel on the stern in front of the rudder. The wheels are powered by pedalboards, and Chinese authors mention that these ships can attain very high speeds.[457]

The ocean-going junk, precursor of the modern sailboat

We have seen that the technological basis of modern sailboats appeared in China during the Han period, 2nd century AD. The elements of this technology were the axial rudder and the modern sail. Navigation develops widely on the Yangtze, in its immense estu­ary, and along the southeast coasts of China. The marking of the coasts with beacons

develops under the Yuan. Junks having multiple masts appear from the 3rd century.

The large ocean-going junk reaches maturity in the 9th century. This is a very large ship having three or four masts, sometimes even six. In the Song period it can exceed 100 meters in length and can carry several hundred people. One passenger, our Tangiers traveler Ibn Battuta, describes it as follows:

“The large junk has twelve sails, the others (i. e. smaller junks) have up to three. The sails are of bamboo, woven together into mats, they are never lowered but always turn according to the wind direction. When the boat is at anchor, the sails remain hoisted, buffeted by the wind. The crew comprises a thousand men: six hundred sailors and four hundred soldiers: archers, shield carriers, crossbowmen who fire naphtha. [….] On the ship there are four decks with bunks, cabins and salons for the merchants.”[458]

In the 11th century the compass appears on Cantonese junks; before it had been used only by astrologists who assured the correct celestial orientation of dwellings. The com­pass makes seafaring navigation far easier. The large junks navigate on the Sea of China and the Indian Ocean toward Korea, the south of India, and the Persian Gulf. The port of Canton is recognized since the time of the Qin Dynasty; it hosts a cosmopolitan com­munity of sailors and merchants from everywhere. Fuzhou, somewhat further north, is another large port. Hangzhou, a port and city that, in the 13th century, earns the admi­ration of both Marco Polo and Ibn BattUta when they visit, is exceptionally prosperous in the period after the retreat of the Song into south China.

At the beginning of the Ming Empire, grand maritime expeditions are launched on all seas to celebrate the new rulers and the eviction of the detested Mongols. These expe­ditions represent the apogee of navigation in imperial China. Between 1405 and 1433 seven expeditions follow one after another, involving an immense fleet of 62 large junks nearly 130 m long and 50 meters wide, in addition to a number of smaller boats. These expeditions are as much diplomatic as commercial, with destinations of Indochina, Java, Sumatra, the south of India, Ceylon, Hormuz in the Persian Gulf, Jeddah in the Red Sea, Aden and the eastern coast of Africa, and perhaps even Mozambique.[459]

But the decline of seafaring navigation in China begins in the 16th century. This decline results from the quasi state monopoly established by the Ming, who authorize only large official expeditions. This decline coincides also with military setbacks in struggles against the Mongols in the north, and with a pullback of the Ming civilization taking refuge in a sort of defensive posture within the borders of China. Western sailors of the 17th and 18th centuries find the Chinese coasts to be infested with pirates, and witness a population turning its back to its coasts.

We have seen the first use of hydraulic energy in China under the Han Empire, at the beginning of the 1st century AD. The Chinese devices are quite complex from the very beginning, in contrast to the comparable but simpler devices developed at the same time in the Roman Empire. There, simple horizontal-axis mills are used to turn a grindstone. But in China there are complex devices powered by vertical-axis water wheels, according to all evidence. These wheels power batteries of pestles for agricul­tural or metallurgical use (21 AD). In the industrial center of Nanyang they power bat­teries of bellows to provide combustion air for the melting and casting of iron (31 AD).

It is probably in the 4th century that the direct use of rotating wheels to grind grain was developed, in response to depopulation resulting from the wars following the fall of the Han Empire. In the 7th century the technology of mills is exported from China toward Korea, Japan, and Tibet. In China of the 8th century one finds many large mills having up to five wheels, the property of rich merchants, Buddhist abbots, imperial concubines and palace eunuchs. Conflicts inevitably arise from competing uses of water: the industrial flour trade, navigation, and agriculture. The Confucian civil ser­vants give priority to traditional uses of water for the general public good, and accord­ingly they issue edicts to limit the proliferation of mills. In 778, eighty mills are destroyed by order of the administration.[453]

Hydraulic energy is thoroughly assimilated into Chinese culture at the beginning of the Christian era, when the use of the water wheel is increasingly widespread. Such uses include the powering of batteries of hammers, forge bellows, mills, and also square-pal­let chain pumps, and even merry-go-rounds of dolls (in 260), celestial spheres (slowly rotating astronomical models) in 590, and textile spinning machines (the first dating from 1313.[454] The noria should, however, be considered separately. As we have said earlier, it is probably a technique imported later from the Near East or India, independ­ently of other uses of hydraulic energy.

Windmills, known in the Islamic world since the 7th century, are apparently intro­duced into China from Turkestan toward the 12th or 13th centuries:

“The people of the west use wind mills as the people of the south use water mills.”[455]

These are vertical-axis mills, as was the case in Persia. In China, the sails of the mills are improved through adoption of the technology of sails for junks.

According to tradition Tu Shih, the prefect of Nanyang, “loved the common people and wanted to lighten their work”. This is why he decided in 31 AD to use hydraulic ener­gy to power forge bellows, as we have seen earlier. Later in about 238 AD it is once again a man of Nanyang who spreads this technique to other metallurgical centers:

“Han Chi, when Prefect of Lo-Ling, was made Superintendent of Metallurgical Production. The old method was to use horse-power for the blowing-engines, and each picul of refined wrought (iron) took the work of a hundred horses. Man-power was also used, but that too was exceedingly expensive. So Han Chi adapted the furnace bellows to the use of ever-flowing water, and an efficiency three times greater than before was attained. During his seven years of office, (iron) implements became very abundant. Upon receiving his report, the emperor rewarded him and gave him the title of Commander of the Metal-Workers.”[452]

Figure 8.20 The double-action piston bellows: a device to provide a continuous draft for Chinese metallurgy. Above: engraving of Chambers, 1757 (ancient archives of ENPC).

To understand the importance of this invention, whose usage becomes rapidly estab­lished in all of China, one must note how far advanced Chinese metallurgy was com­pared to that of the West.

Melting and casting were practiced in China very early. The key to this metallurgy is the quality of the furnaces and the draft of forced (blast) air that makes it possible to attain elevated temperatures. An illustration dating from 1313 shows the bellows mech­anism powered by hydraulic energy (Figure 8.19). This consists of a horizontal water wheel at the upper end of whose (vertical) axis another horizontal wheel is fixed. Around this latter wheel there passes a belt that drives a third, smaller wheel, which therefore rotates more rapidly. The axis of this small wheel has an eccentric arm on which a cam pivots, thus introducing a rapid alternating movement which in turn activates the bellows.

The bellows itself was initially nothing more than a skin sack fitted with an outlet pipe for the air. Over time, wooden walls are added, and the bellows evolves into an extremely efficient device whose first known description dates from 1280. This was a double-acting bellows, consisting of a piston sliding in a parallelepiped that is divided into two chambers by the piston (Figure 8.20). As the piston moves back and forth, the air in one of the chambers is always being compressed. The evacuated air circulates through a secondary compartment, then into an exit nozzle with a pivoting flap serving as a check valve. Two such check valves also act on each end of the compression cham­bers. The edges of the piston are covered with feathers or paper to limit air leakage. This remarkably simple device delivers a continuous supply of blast air.

Water lifting machines respond to a very basic need of civilization – that of raising water from a river, canal, or cistern for its distribution to agricultural or urban uses. The Near East had used the shaduf (Figure 2.4), a balance-beam device, for a very long time – but this device was not used in China. We have seen that more sophisticated devices appeared in Egypt during the period of Alexandria (the end of the 3rd century BC), then in the Roman Empire. Examples include the Ctesibios pump (Figure 5.5), the Archimedes screw (Figure 5.3) and the muscle-powered lifting machine (Figure 6.20).

The first written evidence of lifting machines in China is found in a treatise of Wang Ching during the latter Han period (80 AD). We cited this treatise earlier in summariz­ing the innovations of the Han period, and here is a specific extract:

“In the streets of the city of Loyang there was no water. It was therefore pulled up from the

River Lo by water-men. If it streamed forth quickly (from the cisterns) day and night, that was 82

their doing”.

Another text from 189 AD is more explicit, again concerning the question of water supply in the capital Luoyang:

“He (the minister Chang Jang) further asked Pi Lan to cast bronze statues… and bronze bells… and also to make (to cast) “Heavenly Pay-off” and “Spread-eagled Toad” (machines) (which would) spout forth water. These were set up to the east of the bridge outside the Phing Men (Peace Gate) where they revolved (continually, sending) water up to the palaces. He also (asked him to) construct square-pallet chain-pumps and “siphons”, which were set up to the west of the bridge (outside the same gate) to spray water along the north-south roads of the

city, thus saving the expense incurred by the common people (in sprinkling water on these

83

roads, or carrying water to the people living along them).”

This text refers to the simultaneous use of several different machines. According to Joseph Needham and his collaborators, the siphons mentioned here are probably simple piston pumps, like those used in China to pump brine from the salt mines. Perhaps other machines in use were manual lifting wheels.

The pump with chain and square paddles (rectangular, in fact), also called the drag­on backbone machine, is explicitly mentioned in the text. It is typical of Chinese inven­tions, and Figure 8.18 gives an idea of its workings. It is a wooden chain fitted with rec­tangular paddles, circulating in a long wooden flume that is open at each end, inclined at 25° or less from the horizontal. Water is lifted by the upwards movement of the pad­dles inside the flume. The chain to which the paddles are fixed was originally powered by men (or young girls) on a pedalboard. But from the 12th century one encounters descriptions of these machines as powered by animals, and even by hydraulic wheels. The lifting height can be of the order of 5 meters.

Rice cultivation developed rapidly under the Tang and the Song, and this agriculture requires intensive irrigation. The authorities favored the dragon backbone machine to lift water into the rice fields. In 828 they even standardized the specifications for this pump, whose great success can be attributed to its ergonomics. In the 12th century its use in Turkestan is noted on the occasion of a voyage of a Taoist wise man, then it appears in Korea in the 15th century. Between the 17th and 19th centuries it is used to various extents throughout the world.[446] [447]

A parallel technology to the dragon backbone machine is the noria. This hydraulic – powered lifting machine is already well known to us – in Chapter 6 we cited the descrip­tion given by the Roman Vitruvius in about 25 BC, and we have seen its very broad use in Syria and in the Arab world. But the history of its introduction in China is an enig­ma. There is clear evidence of the use of hydraulic energy in China ever since the begin­ning of the Christian era, but the Chinese hydraulic wheels appear to be mostly horizon­tal, with vertical axes. The noria appears in Japan about 800, but one cannot find seri­ous evidence of its use in China before the 10th century, and indeed there is no indis­putable evidence prior to 1130. When one encounters the noria in Korea in the 15th cen­tury, it appears as an alternative lifting technology to the square-pallet chain pump, and it comes from Japan, not China.[448] These observations suggest that there may have been

two pathways for the introduction of the noria in Asia: by land in the region of the upper course of the Yellow River in China on the Silk Road around the 10th century; and in Japan by sea from India two centuries earlier.

In his account of his Voyage in China (1345), Ibn BattUta describes wheels on the Yellow River that appear to be norias:

“(The Yellow River) is lined with villages, cultivated fields, orchards, markets, in the manner of the river Nile in Egypt; but here the land is more flourishing, and on the river there are a large number of hydraulic wheels.”[449]

The Chinese noria is very light, made of wood and bamboo, and therefore it can be turned by a weak current. The most famous of these wheels are those in the region of Lanzhou on the upper course of the Yellow River. Some fifteen meters tall, they are arranged in batteries or sets of up to ten per row.[450]

We have seen that the bucket chain or saqqya was widely used in the Arab world. But it was used only marginally in China, and then probably only in the salt mines of Sechouan at a relatively late date.[451]

The major city of Hangzhou, prominent in the account of Marco Polo as we have seen, is located at the head of an estuary that is nearly 100 km long. The land there is quite flat and thus exposed to the tidal surge and waves associated with strong storms. Moreover in this particular estuary there is an additional extraordinary phenomenon: one of the largest tidal bores in the world.

The tidal bore is a wavelike disturbance, or a series of disturbances, resulting from the progressive steepening of the tidal wave as it propagates into a sufficiently long and shallow estuary. At Hangzhou in the Chien-Thang estuary the mean height of the bore is the order of two meters. But during equinox tides, it can reach 7 or 8 meters. It is very special to be able to come to see this bore during extreme tides, a truly festive occa­sion. Here is a poetic description dating from the 13th century that gives some idea of the power of this phenomenon:

“The tidal bore on the Che River is one of the great sights of the world. It reaches its full force from the sixteenth to the eighteenth of the month. When it begins to arise far away at Ocean Gate, it appears but a silver-thread; but as it gradually approaches, it becomes a wall of jade, a snow-laden ridge, bordering the sky on its way. Its gigantic roar is like thunder as it con­vulses, shakes, dashes, and shoots forth, swallowing up the sky and inundating the sun, for its force is supremely vigorous. “[441]

Figure 8.16 The city of Huzhou, near the south bank of Taihu lake. This city is linked to Hangzhou and to the Grand Canal by a network of canals. “It is one of the largest and most considerable cities of China, due to its richness, its commerce, the fertility of its land, and by the beauty of its waters and mountains.” (du Halde, 1735 – ancient archives ENPC).

The earliest land protection works along this estuary date from the time of the latter Han, around 85 AD. The name of the estuary, the estuary of the dike of coins, also dates from this period. The first builder of the dike was the governor of the region called Hua Hsin. He had called upon the people of the region to bring earth and stones for the proj­ect, for which they were paid in coins. The dike is exposed to the force of the waves, and the sea apparently destroyed the first few attempted structures. There ensued debates on the mode of construction that should be adopted. Should the dike be built of earth with a rock armor layer, a costly solution? Or should it be built more simply of earth mixed with straw and brush, as were many other dikes and dams? One can also imagine a structure based on rocks contained in bamboo cages, anchored with stakes and stabilized with iron chains, an assembly commonly used to repair fluvial dike breaches. Work was conducted in 910, in 1014, again in 1035, then again in 1169…. Gates were put in place to let the water flow seaward at low tide.

A continuous rock dike supported by an earth fill is eventually achieved in 1368. In the Ming Dynasty, in 1448, a solution is finally found that has remained satisfactory up to the present time. This consists of constructing a wall of cut stone interconnected with steel pins and with a stairstep profile facing the waves, better to break their force. Its foundation is made of wood piles, and the wall leans against old rock outcrops as well as against an earth fill.[442] [443] This type of construction is similar to that used for the large dike of Hongze lake described earlier.

80

Initially this maritime dike was probably about 80 km long. Today, it is more than

350 km long, and its crest rises more than eight meters above sea level.[444] [445]