Water Management in Saudi Arabia: The Ancient Dams

Description

Water management represents the most critical and imperative condition for the development and prosperity of human societies. In Arabia, after several moisture episodes throughout the Early/Middle Holocene period, a Rapid Climate Change (RCC), activated around the 4^th millennium BCE, has resulted in a severe decrease of annual precipitations, and an overall aggravated aridity that challenged agricultural development in most of the territory. This situation triggered human innovations and adaptive behaviours to counter water scarcity. The development of technologies such as wells, qanat, birkat (cisterns) and water diversion systems, permitted humans to live in the Peninsula, despite its extreme conditions, through the emergence of oases based on water catchment and control where sustainable agriculture could be practiced. While these irrigation techniques were used since the 3^rd millennium BCE, large-scale dams in the region were developed much later, in the first centuries CE.

Dams are “barriers built across a river in order to stop and retain the water from flowing, making large surface reservoirs.” They require a distinct type of technology, in terms of scale and ambition. In Arabia, they notably aimed to capture the rainwater made available during torrential rainfall or wadi flooding, playing a double role: to avoid the destructive impacts of floods on human settlements; and collect and use scarce and precious rainwater. To achieve those key objectives, dams required advanced hydro-engineering skills. They mobilised a precise knowledge of local topography, a deep understanding of the properties of construction materials, architectural/engineering knowledge to ensure their resistance, and familiarity with hydrology and water distribution systems to bring water to agricultural fields and wells.

In addition, the construction of dams required significant financial resources, an advanced social organization, and a considerable labour force. Dams, therefore, could appear only under specific geopolitical context, characterized by a strong and centralized decision-making system that could canalise the necessary collective efforts and allocate sufficient resources to build and maintain large-scale infrastructures that aimed to prioritise agricultural productivity.

The elements included in the serial property illustrate both the human ingenuity deployed into hydro-engineering prowess, and the emergence of what can be called hydro-states as a political culture, in a context of environmental distress.

About two dozen of ancient dams are known in the regions of Taif (65 km East of Makkah) and Khaybar (150 km North of Madinah) that form the two major clusters where ancient dams are found.  Water Management in Saudi Arabia: The Ancient Dams serial property includes 5 of these ancient dams. Two among them, Sadd al-Hasid and Sadd Al-Bint, probably pre-Islamic, are in the fertile region of Khaybar; Sadd Al-Khanaq, located in the vicinity of the holy cities of Madinah dates from the Umayyad period, while Sadd Samallaqi, which might be pre-Islamic, and Sadd Al-‘Aqrab are located near the city of Taif. All these dams were erected to develop agriculture. They reflect diverse engineering designs and tell complementary stories about the development of the dam technologies, in the light of specific environmental and political contexts. The five dams offer a highly visible testimony of advanced hydro-engineering skills, but the understanding of the irrigation systems articulated around them — including canals, complementary dikes and sluices, and surrounding irrigated fields — has still to be consolidated and opens fascinating avenues for future research.

Sadd Al-Bint

Sadd Al-Bint, literally “the dam of the girl” is located 30 km south of the oasis of Khaybar. Its name, as well as its date, spark scientific debate, nourishing local imagination which, based on architectural similarities between Sadd al-Bint and Marib Dam in Yemen, invoke a contemporary origin of the two and attribute the “girl” dam’s identity to the Queen of Saba’.

The dam is possibly pre-Islamic or early Islamic. Its monumental dimensions are unrivalled, with a height of 30 m and an original length of about 208 meters. Although partially collapsed, the standing part of the dam is still 135 m-long. The structure, made of local black basalt boulders is tapering due to the double step, both on the upstream and downstream sides, making its base larger and progressively shrinking in width until the crest of the dam, where a broad walkway, secured by a 1 m-high wall, is found on the upstream side. Beside its outstanding proportions, Sadd Al-Bint is of utmost interest for its slightly curved plan. This design technique, first developed by the Romans, aims to control the water load pressure, and distribute it more effectively to avoid localized tension on the walls. It is a sophisticated engineering solution requiring extensive hydraulic engineering competences. The upstream side, in contact with the collected water, is fully plastered for waterproofing. The breach created by the collapse of the north-eastern part of the dam permits to observe the composition and evolution of the dam showing that successive layers of walls were added for reinforcement through time. Some of these layers were plastered on the downstream side too, although the latest layer, which constitutes the downstream side nowadays, shows no traces of plaster. Sadd al-Bint also counts several complementary hydraulic structures offering interesting opportunities for research. Among them, the two walls running perpendicular to the dam at its western end, and the still partially unstudied system of overfull canals regulating the amount of water kept by the dam.  Still unclear is also the scope of the steps originating from the walkway of the dam’s crest, leading down into a space on the edge of the downstream side of the dam where there was no water. The water channels, bringing the water from the dam to the fields located a few km away, formed a complex hydraulic system that is still partially unstudied and unexcavated.

Sadd Al-Bint is particularly interesting for its monumental dimensions (with its 30 meter it is the highest dam in the region), its innovative curved design exceptional in the region, its complex hydraulic solutions, and its importance in the collective imagination and local community self-identity.

Sadd Al-Hasid

The oasis of Khaybar, located 150 km north of Madinah near the lava field of Harrat Khaybar, has hosted a nearly continuous human presence since prehistoric times. Its specific volcanic geology, characterized by the presence of impervious underground basalt layers which capture the water without absorbing it, allows the clay soil to remain moist and results in the formation of numerous natural water springs. These favourable environmental conditions allowed human communities to develop a vibrant agriculture in the region, that became renowned for its date palm groves.

Sadd Al-Hasid is located 14 km south of Khaybar. It is composed of two separate dams, located a few hundred meters apart, forming a twin system of water retention creating a large basin for irrigation. Both the dams were judiciously established at the narrowest points of a relatively large wadi. Although the absence of inscriptions prevents to date them with certainty, they might date from the pre-Islamic period. The northern one has a total length of 60 m and reaches a height of 10 m. Its structure was carefully designed: the dam is stepped on both the upstream and downstream sides, to consolidate its base that is submitted to stronger pressure than the top, and possibly also to enable easier access for maintenance and repair. The upstream dam wall is topped by a walkway secured by a ramp wall. In the middle of the downstream wall, at the base of the structure, a high arched opening leading into a passageway (now blocked) permitted to control the water flow. This type of outlet, located at the base of the dam, constitutes an ingenious solution to evacuate excessive water and remove sediments accumulating at the bottom of the dam. The builders of the dam used construction material sourced locally, as the dam is entirely made of well-cut basalt blocks. It was restored in 1974-75 and strengthened with concrete, to keep it functional.

The southern dam, that has not been restored, is less imposing and less high (its base is covered with silt), but it still presents traces of the original plasters and mortars on the stepped upstream façade. Remains of a lateral water outlet, to control water flow, are also partially preserved. Sadd al-Hasid twin dams are still functioning and continues to retain water although the lands around it are now too salty to be cultivated. In addition to its smart engineering and architectural design, this twin dam stands out for its exceptional longevity and continuous maintenance through time.

Sadd Al-Khanaq

Sadd Al-Khanaq stretches across a tight corridor between two mountains, in Wadi Al-Khanaq, 15 km east of Madinah. Its total length of 43 meters makes it the smallest among the dams included in the serial property. Carefully located at the narrowest point of the wadi, to optimize the construction effort, this dam shows a perfect imbrication in the surroundings and an ingenious use of existing natural elements. Its height (17 metres, making it the 2^nd highest dam of the series after Sadd Al-Bint) coincides with the height of the two mountains that encase the dam, while its length is “limited” to 43 m thanks to two protruding cliffs on both sides of the valley that form two natural shoulders providing a solid foundation for the wall structure at both ends. The discovery of an ancient industrial area north-west of the site - quarries from where basalt stones were extracted, moulds for the preparation of red bricks, and equipment for the preparation of the lime mortar - proves that construction materials were extracted nearby and shaped by the labour force in the vicinity of the dam.

Sadd Al-Khanaq stored the water blocking the course of the wadi flooding through the gorge. A smaller dam, lower and less massive (originally 56 m-long with a maximum width of 11 m at its basis) was erected 300 m to its west. The twin dams formed an artificial lake, some 1,600 m in length and 350 m in width that had an initial storage capacity of up to 560,000 m³. Sadd Al-Khanaq is built with a double-faced wall made of large well-cut blocks and a core composed of basalt rocks mixed with gravel and bound with a strong lime mortar. The southern façade, which was in contact with water, is entirely lined with courses of fired bricks and further protected by impervious plaster to prevent water penetration. The northern façade, downstream, is lined with large stones. Like Sadd Al-Bint, also Sadd al-Khanaq is stepped on both the upstream and downstream sides, to increase resistance at the basis. Its width reached 17 m at the base and 12.7 m at the top. The western smaller dam displays a similar masonry characterized by large basalt stones and a plaster layer on the side exposed to water. It is worth stressing that although both twin dams have collapsed in their middle, this was not due to water pressure, but a result of earthquake and volcanic activity.

A Kufic inscription dating from the time of its construction designates the Umayyad Caliph Mu’awiyah bin Abi Sufyan (who reigned between 661 and 679 CE) as the sponsor of these dams that were of utmost importance for the development of Madinah region. Further research is needed to better understand how the water was distributed from the artificial lake, as no traces of ancient canal remains are known. The presence of several wells in the surroundings and in the nearby ancient settlement might indicate that an underground channel linked the wells to the water stored in the lake.

The heritage value of Sadd Al-Khanaq lies in the outstanding knowledge of the local topography that underpinned its creation, and in the remarkable ability of the Umayyad rulers to modify the natural environment by building a dam completely integrated into the natural mountainous landscape capable to create a large artificial lake. In addition to these key features, Sadd Al-Khanaq preserves important archaeological traces of the technical processes that enabled its creation and has preserved an important inscription proving its date and its relevance for the Umayyad rulers.

Sadd Samallaqi

Located 30 km south-west of Taif, Sadd Samallaqi lies in the fertile Wadi Thumalah valley where farms and agricultural activities thrive until today. The dam was built between two mountains at the narrowest point of the Wadi. Its present height is about 10 m. Yet, extensive silting, partly removed in the 1950s, has led to successive additions that raised the height of the water retaining wall over time. Sadd Samallaqi is the greatest dam of Taif region (more than 210 m long) and is in very good condition, as most of its walls are still standing.

It was built with the traditional double-faced wall masonry technique, with a core backfill. Its walls are made of large rectangular and regularly cut stone blocks and its upstream side was covered with a solid waterproofed plaster. At the top of the dam, the wall is 2 m wide. The downstream side forms narrow steps and a 12 m-wide spillway was cut through the rock. About 25 m away from the dam, are found two historical wells, connected to the dam by a canal running directly towards the dam.

Like for Sadd Al-Bint, architectural similarities with Saad Marid in Yemen have spurred hypotheses of an origin related to the Kingdom of Saba’ in Yemen. While more investigation is needed to date and precisely assess its origins, Sadd Samallaqi is believed to be pre-Islamic, even though the presence of Early Islamic Kufic inscriptions on the dam boulders proves that it was used and continuously visited in Umayyad times.

Its longevity, due to continuous maintenance efforts to counter silt, the interesting mix of periods and influences it displays, and its integration in the surrounding area with the canal connecting it to historical wells contribute to the heritage significance of this ancient dam.

Sadd Al-‘Aqrab

Sadd Al-‘Aqrab, positioned on a northwest/southeast axis, is built with a technique similar to other dams of the Ta’if area with two thick parallel stone walls filled with rubble. Each wall is 1 m thick with 3 m of fill. Most stones and boulders used for the two parallel walls are large blocks, randomly coursed and laid dry. The dam is 113 m long, 4 m high, and 5 m wide with steps on the downstream side. It is well preserved as the dam’s wall suffered no major collapse, but the upstream side is covered with silt and sediments.

Three low walls forming obtuse angles on the upstream side, were constructed on each end of the dam’s main wall to divert the water. The water diversion wall built at the northern end of the dam is 16 m-long, 1 m-high and 1 m-wide; while the two adjoining diversion walls built at the southern end of the dam, across a rocky outcrop, are respectively 35 m-long and 29 m-long and therefore constitute significant length additions to the dam. Sadd Al-‘Aqrab main specificity relates to the presence of a water channel (0.8 m wide) built at its centre. Smooth flat stones line the bottom of the channel, and form four steps. As for the rest of the dam, the slabs were laid dry without mortar. About 3 km southeast of the dam is an old town and a cistern with a still active qanat system.

Justification of Outstanding Universal Value

Dams are major engineering and technological structures aiming to increase (or establish) agricultural production. They had an important economic and environmental impact on the territory and were related to specific governance systems. They were originally developed in green areas, where cultivation was already made possible by favourable climatic conditions. Water Management in Saudi Arabia: The Ancient Dams series is consistent with this observation: Khaybar is an old-established oasis renowned for its fertility; and the other dams of the series are all strategically located across Wadis, which drained rainwater and created verdant areas. The erection of dams that increased agricultural productivity, and prevented flooding disasters, created a new pattern of occupation of the territory favouring the adoption of permanent or semi-permanent sedentarism.

The dams of this series are rooted in a more ancient technological tradition dating from the early 3^rd millennium BCE. The Kafara Dam, in Egypt, and the Jawa Dam in Jordan, display the vestiges of this early dam development phase. Sadd Kafara’s construction materials were not watertight, leading to its fast erosion and early collapse. By the end of the 3^rd millennium BCE, dams also emerged in Mesopotamia. The Nimrud Dam across the Tigris River, a key achievement of this period, aimed both at reducing erosion and controlling floodwaters for later use as irrigation water. In Southern Arabia, the Pre-Islamic Himyarite civilization developed dam technology between the 1^st century BCE and the 4^th century CE. The Marib Dam is one of the most famous examples from this culture, but more dams from the same period are found in the western mountains of present-day Yemen.

Water Management in Saudi Arabia: The Ancient Dams serial property clearly reflects the interchanges of hydro-engineering expertise with earlier and contemporary constructive traditions and experiences. Like the Sadd Kafara, Nimrud Dam, and South Arabian dams, the elements of the series are all gravity-dams acting by the volume and the mass of aggregated construction materials. Their structure is generally based on the edification of two parallel walls, forming respectively the upstream and downstream side. The gap between these walls is filled by a substantial and compact amount of rubble, aiming at increasing the weight and resistance of the whole structure to load pressure. Their walls are generally stepped, sometimes both on the upstream and downstream sides or only on the downstream side, creating a greater width at the base progressively shrinking toward the crest. This technique strengthens the base of the dams that is subjected to higher pressure. The integration of spillways and outlets into the wall, to evacuate excess water and empty the dam to remove accumulated silt, is an additional characteristic widely shared among the elements of the series. Construction materials were usually sourced locally and selected for their solidity; stone and fired bricks were selected and masterfully used in the construction of the Arabian dams. These dams show a precise knowledge of the local topography resulting in impressively judicious location choices, and Sadd Al-Bint displays an original slightly curved design that might relate to techniques and hydraulic know-how developed by the Romans.

The monumentality of the elements of the serial property illustrates the role dams played not only in mastering a harsh environment, but also in participating to the emergence and strengthening of new centralized states. This was probably the case also for the pre-Islamic dams (as in the case of the Yemeni dam of Marib, with which Sadd Al Bint and Sadd Samallaqi are sometimes affiliated, that was a pride and identity symbol of the Kingdom of Saba’), but more research on these structures is needed.

Water Management in Saudi Arabia: The Ancient Dams serial property documents a major achievement of human creativity and engineering that favoured the development of societies based on water management in arid climatic zones and supported the urbanization process and the development of state-based human communities.

The revenues generated by the Umayyad conquest were partly invested in agricultural development plans in the Hejaz. Sadd Al-Khanaq inscription mentioning the Caliph Mu’awiyah ibn Abi Sufyan shows that this dam was not just a mere water supply infrastructure, but also part of a larger royal plan aiming to integrate the population of Arabia into a state pattern, where the ruler had to be able to meet the water and food needs of the population and where social classes get structured around the possession of real estate near water infrastructures. The dams edified in the Umayyad period reflect the strategy of the new elites based in Damascus that needed to strengthen their presence and legitimacy in the Arabian territory, notably around the holy cities of Madinah and Makkah.

Water Management in Saudi Arabia: The Ancient Dams opens a fascinating window of opportunity for future research as in most cases the authority in charge of their construction, their date, the identity and status of engineers and the labour force, the area and ownership status of irrigated lands and the other components of the irrigation systems complementing the dams are still unknown.

The Outstanding Universal Value of the serial property stems from the engineering prowess and knowledge of local environment, which reflect human genius, human adaptation to the environment and interchange and evolution of technical competences. Its OUV lies in the acknowledgement of the exceptional constructive and hydrologic know-how that permitted their creation, and in the recognition of the positive environmental impact ancient dams had, supplying water for several generations in arid territories and permitting the development of agricultural production in extreme climatic conditions. Their remarkable longevity results from both the engineering quality of their original construction, and the maintenance efforts perpetuated by posterior communities of users. The narrative also sheds light on the discontinuous centralized hydro-state culture that cyclically emerged as a response to arid climate and a specific environmental context.

Criterion (ii): The dams of the serial property are part of a broader technological tradition reaching back to the Ancient Egypt. The elements of the series show the influence of South-Arabian, Egyptian, Mesopotamian, and Roman dam-building technologies and know-hows in Arabia. Sadd Al-Samallaqi and Sadd Al-Bint share the monumental scale of the South-Arabian Dam of Marib and popular legends commonly attribute them to the Queen of Saba’. Though this attribution needs to be scientifically proven, the technical characteristics of the Water Management in Saudi Arabia: The Ancient Dams attest a common technological tradition and demonstrate the cultural interchanges in the region. The 5 elements of the series are gravity-dams made up of two parallel stone masonry walls filled in the middle by rubble, but they have different technical and constructive characteristics: some used lime mortars and were coated with plaster, others are constructed in dry stone masonry, while others are of solid stone masonry, or a combination of stone and fired bricks. The presence of water channels to bring water to the fields, and of diversion walls to evacuate the excess water and ease load pressure, attest the constructive know-how of their builders, and the technical evolution of dams across time and space.

Criterion (iv): The stone and firebrick dams built in Arabia in the first centuries CE and in the Umayyad period are outstanding examples of a building typology that was progressively developed in the Middle East and in other parts of the world to control and distribute water to urban and rural areas. More ancient dams and dikes were built in compacted earth and in wood, but the progressive development of building technologies permitted to create impressive stone masonry dams rising for tens of meters and forming vast water reservoirs. A relevant contribution to dam engineering was developed by the Romans who built arched dams and profited of the quality of their mortars and cements. The ancient Arabian dams — notably Sadd al-Bint with its unique plan (probably developing Roman models) and its profile resulting from successive constructive phases — form an impressive ensemble and include one of the most monumental and higher pre-modern dams.

Criterion (v): Water Management in Saudi Arabia: The Ancient Dams reflect the ability of human communities to innovate, confronting severe climatic conditions. The dams of the series materialise the depth of the geographic and hydrological knowledge of their builders, who were able to take advantage of the scarce rains to accumulate large amount of water in seasonal reservoirs that fed large agricultural fields and permitted the economic development of the region. The systematic choice of the narrowest points along the wadis, the perfect encasement of the Khanaq dam in the surrounding mountain chain, the use of local stones, and the careful selection of the most advantageous sites to erect a dam and create water reservoirs in the vicinity of agricultural areas, demonstrate the sound knowledge and technical awareness that underpinned the construction of these extraordinary structures. Their longevity constitutes the best evidence of their strong impact that allowed to improve water availability to generations of users. Though Sadd Al-Khanaq and Sadd Al-Bint partially collapsed and are now unable to serve their primary function, Sadd Samallaqi is still intact, and Sadd Al-Hasid is still standing and has been upgraded in the 20^th century.

Statements of authenticity and/or integrity

Authenticity

The elements of the serial property include five major sites among the tens of ancient dams found in Saudi Arabia. The attributes of these elements underline the property’s historical complexity - from pre-Islamic to Umayyad state’s consolidation - its geographical diversity, and its diversity of form and design. The numerous attributes borne by each component of the series represent the diversity of historical and geographical contexts, designs, and longevity that jointly materialise the cultural value of this serial property.

Dams require continuous maintenance efforts, and the ones included in the series received consolidations and additions to counter erosion and silting, until they fell into disuse. Since their abandonment, the dams of the series did not undergo reconstructions of the archaeological remains (apart from the northern dam of Sadd Al-Hasid that was reinforced with concrete in the 1970s to allow the continuity of functional use). Their material conditions are therefore fully authentic.

Sadd Al-Bint stands out as the major monumental element of the property. Its attributes relate to its unique monumental scale, to its building technology and the quality of its masonries, and to its innovative curved design reflecting the development of new hydro-engineering skills in the Arabian context. Its legendary attribution to the Queen of Saba’ gives this site an additional value ideally connecting ancient Khaybar with the ancient South-Arabian Kingdoms. Its geographic position, 2 km from the nearest agricultural fields south of Al-Thamad, proves its essential role in regional agricultural production. Until today, the remains of the dam are occasionally watered by seasonal flooding. The wild vegetation that thrives at the feet of the dam proves, even in its present ruined conditions, the soundness of its edification in this precise spot.

Sadd Samallaqi, that shares with Sadd Al-Bint similar monumental dimensions and legendary origins connecting it to the Kingdom of Saba’, lies in a region where farms are still active thanks to a favourable humid micro-environment. By its location and continuing role, it proves the validity of dam technology in Arabian context over millennia.

Sadd Al-Hasid and Sadd Al-Khanaq share a similar twin-dam concept. This technical solution/design is an important attribute of these two dams which illustrate the “form and design” diversity of Water Management in Saudi Arabia: The Ancient Dams. Both dams are based on a twin-dam system which allow the formation of a large artificial lakes. But they also show other distinct attributes that set them apart. Sadd Al-Khanaq is rooted in an Early Islamic context and bears an inscription revealing its inclusion within a royal project carried out by the Umayyad Caliph Mu’awiyah bin Abi Sufyan; while Sadd Al-Hasid is probably a pre-Islamic construction representing a different historic moment and social organisation.

Integrity

Tens of ancient dams are found in Saudi Arabia. The selected elements of the series illustrate their cultural values and include a sufficient number of elements to express the potential OUV of the series and ensure the complete representation of the features and processes which convey the property’s significance. Furthermore, the 5 elements, though partially ruined, present an overall good state of conservation and are not affected by adverse effects related to unsuitable developments of their surroundings or to the neglect of the vestiges. Their isolated position, far from modern urban centres has guaranteed the long-term preservation of the vestiges and of their natural setting. These five dams have notably preserved their relationships with the landscape that is essential to understand their function, relevance, and distinctive character.

The proposed elements, selected among a larger group, offer a complete representation of the diversity of the dam infrastructures across central Arabia, each contributing to the potential OUV of the series. The selected structures share a direct testimony, conserved and transmitted till the present day, of the hydro-engineering skills developed in Arabia. The evocative power of their attributes is intact: they attest the interchanges of techniques and provide a remarkable example of human adaptation to the environment, notably in the advent of aggravated climatic conditions.

Comparison with other similar properties

Most ancient civilisations rose thanks to their capacity to control water distribution to develop agricultural production permitting the accumulation of wealth and favouring urban development. This was notably the case of Mesopotamia and Egypt, Rome, and ancient China, where multiple water management techniques and dams were developed since early antiquity. The World Heritage List counts multiple properties relating to this theme.

In the recent years, the cultural heritage of water is being more and more acknowledged and valued at the international level, as the impact of climate change, and more particularly the advent of droughts, flooding generated by extreme rainfalls, and the overall aggravated scarcity of natural resources, have imposed this theme as a crucial challenge for current and future generations.

The 2015 ICOMOS report Cultural Heritages of Water: The cultural heritages of water in the Middle East and Maghreb has drawn attention to the relevance of sustainable traditional water management practices in the region. Although the World Heritage List already includes several sites related to outstanding hydro-engineering works and sustainable traditional water management in the Arab and Muslim world, (such as the aflaj irrigation system in Oman and in Al-‘Ain oases, or the Persian qanat-s), ancient dams are barely represented in the List.

At the regional scale, the following World Heritage and Tentative Listed sites directly relate to water management heritages and hydro-engineering construction. They provide an important comparative reference.

Petra (Jordan, 1985, criteria i, iii, iv): Inhabited since prehistoric times, this Nabataean caravan-city, situated between the Red Sea and the Dead Sea, was an important crossroads between Arabia, Egypt and Syria-Phoenicia where ancient Eastern traditions blend with Hellenistic architecture. Petra is half-built, half-carved into the rock, and is surrounded by mountains riddled with passages and gorges. The Outstanding Universal Value of Petra resides in its elaborate carved tomb facades and its religious and public architecture, but also in its impressive water management system materialized by cisterns, reservoirs, and channels that formed a vast network controlling and conserving seasonal rains. The archaeological site of Petra also includes a diversion dam protecting the siq from flooding and diverting the water to a 90m-long tunnel.

Shushtar Historical Hydraulic System (Iran, 2009, criteria i, ii, v): The Shushtar system is a homogeneous hydraulic system, designed and completed in the 3^rd century CE. It includes infrastructures for both urban supply and agricultural irrigation uses, ranging from diversion canals to bridges, basins mills, tunnel, operation tower, etc.

Archaeological site of Marib (Yemen, TL 2002, criteria i, ii, iv): With an expanse of 98 hectares, the Sabaean capital Marib was the largest ancient city in South Arabia and is considered one of the most significant historic sites on the Arabian Peninsula. Despite climatically unfavourable conditions, at the end of the 2nd millennium BCE, a complex society emerged in Marib thanks to a highly developed irrigation system. Due to its economic prosperity and geographic location, Marib became the most important trading station along the Incense Route. From their capital Marib, the Sabaeans controlled large parts of the Peninsula and the trade on the incense route as far as the Mediterranean and Mesopotamia. Marib hosts several important cultural sites such Bar´an Temple, Awam Temple with necropolis, Wadi Ghufaina settlement and al-Mabna dam, the Great Dam of Marib, which is considered as a wonder of technical engineering and appears in a verse of the Qur’an. The 650 m-long earth dam of Marib was approximately 15 m high, and had two stone-built tower-like floodgates.

Abdulkhan Bandi Dam (Uzbekistan, TL 2008, criterion iv): The dam is a Middle-Ages ancient reservoir built on the order of ruler of Bukhara, Abdullah II, on the Beklarsay river (Biglar in Russian). It was made of shale and connected with stone slabs and a water-resistant mortar. Constructed at the narrowest point of the river canyon, it was 73 m-long and 15 m-high. The turbulent river broke the dam and today only two third of it remain. A modern dam has been built practically at the same point (Akchabsay reservoir).

Khanbandi dam (Uzbekistan, TL 1996, criteria i, ii, iii): Khanbandi dam is situated in the Zarafshan river basin. 8 channels with 680 dams were built in the 10^th - 13^th centuries CE in Samarkand area, but only 4 dams of such scale are still preserved. The dam of Khanbandi was built at Oslan in Pasttaga gorge. Upper length is 57.75 m, lower is 24.35 m for a height of 15.25 m. The dam is built with granite slabs. Nine cone-shaped holes positioned at different altitudes regulated the water flow. The basis of the dam is 4 times thicker than the top. The length of the created reservoir is 1.5 km, the width is 52 m near the dam and 200 m near the gorge.

Water Management in Saudi Arabia: The Ancient Dams answered to irrigation agricultural needs. On the contrary, Shushtar Historical Hydraulic System, Petra and the Archaeological site of Marib are intrinsically linked to an urban project, if not a royal capital one, and their status and destiny cannot be separated from the ones of the capital-city. Just like Roman aqueducts, Shushtar Historical Hydraulic System provides an outstanding example of hydro-engineering prowess, serving firstly urban needs. Similarly, the famous Dam of Marib included in the Archaeological site of Marib is strongly linked to the pride and identity of the city dwellers. Accordingly, it is the whole site of Marib, and not just its dam, that is proposed for World Heritage inscription. On the contrary, the ancient dams of Saudi Arabia, are found in agricultural areas, and although two of them bear royal inscriptions, they are only indirectly related to urban royal development projects.

Beside the dams acknowledged in the World Heritage Lists, a series of other dams dating from the Umayyad period in Syria and Jordan needs to be considered for their similarities with the elements of this series. The most relevant are:

The Harbaqa Dam (Syria): Part of the Umayyad palace complex of Qasr Al-Hayr Al-Gharb, Harbaqa dam is located across a seasonal watercourse, near the northern mouth of the wadi Al-Barida. It is a straight-walled gravity dam, 345 m long and 20.50 m high with a width of 18 m at the basis that shrinks to 6.30 m at the crest. It is built of large ashlar blocks, bound with lime mortar, forming large steps on both sides, and resulting in a tapering design. The downstream side is strengthened with buttresses; no outlet to evacuate excess water is present. Its monumental dimensions make it the largest dam in the Near East before modern times.

Umm Al-Walid and Wadi Al-Qanatir Dams (Jordan): The twin dams of Umm Al-Walid and Al-Qanatir are located on the same seasonal watercourse and are separated by 1 km. The upstream dam is 135 m long and 9 m high with a width of 6.10 m at the basis and 4.50 m on the crest, as it is stepped on the downstream side. It is made of rectangular limestone blocks cemented with mortar. The downstream side of the dam is strengthened by an imposing 15 m long and 1.20 thick buttress. The solidity of the dam is further reinforced by an embankment that rises to mid-height of the downstream side. The dam has been upgraded through time to counter sedimentation. The second twin dam, located downstream, is a similarly designed straight-walled gravity dam. It is 187 m long, 7 m high and 4.20 m wide at the basis and 3.25 m wide on the top. The downstream side is reinforced by a 20 m long and 0.80 m large buttress. It has an approximately 40 m-long breach in its centre, probably due to the joint damage of erosion and infiltrations into the masonry after the infrastructure was abandoned.

These other Umayyad dams are situated in the vicinity of newly established palaces and agricultural settlements developed in Syria and Jordan by the Umayyad rulers in the 8^th century CE. From the technical point of view, they share many similarities with Water Management in Saudi Arabia: The Ancient Dams. They are particularly relevant from the comparative perspective because they have often preserved part of the original system of canals and outlets permitting to distribute the water retained by the dams into the nearby fields that are no more visible in the dams of the proposed series. Their natural setting, however, is less dramatic than the Saudi desert landscape and their height is lower than the one of Sadd al-Bint.

Water Management in Saudi Arabia: The Ancient Dams serial property sheds light on the development of dams that cyclically emerged as a response to the constraints of an arid climate, through centralized decision-making processes and collective efforts. The series includes 5 of the most impressive and better-preserved constructions known to date, among the tens of historic dams found in the Taif, Madinah, and Khaybar regions of the Kingdom of Saudi Arabia. The number of ancient dams reflects not only the deep understanding of the local geography and topography but also an overall integrated territorial planning approach (especially during the Umayyad period) aiming to increase the agricultural productivity of an arid territory.

The stakes of Water Management in Saudi Arabia: The Ancient Dams are different from the ensemble of sites presented above and are strictly correlated to a specific geographic context, as these dams played a major role favouring the transition from partially mobile lifestyles to urbanization and sedentarism, in a context of climatic distress.