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In the Middle Ages, in the Zarafshan oasis, in addition to traditional earthen dams, complex engineering structures made of baked bricks, natural stone, and water-resistant hydraulic mixtures  were widely used. Studying the ancient hydraulic constructions in the Jizzakh oasis  and its surrounding areas provides insights not only into the regional history of irrigation but also into the evolution of medieval water management technologies across Central Asia . Such structures serve as an important resource for researchers and tourists, offering a window into the historical dynamics of the region.   Archaeological Research and Sites Between 1950 and 1962, the Mokhondaryo Archaeological Expedition  studied a number of reservoirs and water distribution structures  around the Zarafshan Valley and the Nurota mountain range. Among these, the Khonbandi Dam  (Forish District) dating to the 10th century, the G‘ishtband Dam (Kattaqo‘rg‘on) built in the 12th century, the Abdullakhonbandi Dam (Oqchobsoy) from the 16th century, and the water-dividing bridges constructed during the Shaybani Khan period hold a prominent place. Additionally, bridges in the Bukhara oasis , such as Puli Chahorminor  and Puli Jondor , also exemplify the engineering capabilities of that era . The Khonbandi Dam  is the oldest structure in the region that has survived in good condition to the present day. It is located in the Osmonsay Gorge of Forish District. The crest of the dam  measures 51.75 meters , while its foundation  is 24.35 meters  wide. The structure has a height of 15.25 meters  and was constructed from carefully shaped granite stones , held together with a special binding mixture. The dam creates a reservoir  that stretches 1.5 kilometers  in length and can store up to 1.6 million cubic meters of water , mainly from spring floods in the spring season. Socio-Economic Impact The water stored by the dam enabled the irrigation of approximately 1,500 hectares  of land along the border of the Kyzylkum  and Mirzacho‘l deserts. The ruins of Kaltepa (ravot) , situated 6 km from the dam, indicate that agriculture and urban culture flourished  in this area during the 10th–12th centuries. However, after the dam fell into disuse, the once-prosperous oasis gradually reverted to desert , underscoring the vital role of hydraulic infrastructure in sustaining regional settlements. Engineering Solutions and Calculations Medieval engineers employed unique methods to control water pressure  in the dam. On the western side  of the structure, nine conical pipes  were installed, which were opened in sequence depending on the water level. The placement of these pipes was carefully designed to dissipate the energy of the water  and to protect the dam’s foundation from erosion , directing the flow toward the surrounding rocks. This demonstrates the advanced understanding of hydraulics and structural engineering  achieved by medieval water engineers in the region. The most remarkable aspect is that 10th-century engineers  were able to accurately calculate the vertical and horizontal pressure forces of the water . This structure was built within the Osmonsay Gorge of Pastog‘ , located 12 km north of the center of Forish District . Technical Characteristics of the Dam The dam measures 51.75 meters  in length at the crest and 24.35 meters at the base, with a height of 15.25 meters  (A. Muhammadjonov, research). According to academic Yahuo G‘ulomov , the dam was constructed from cut granite stones , which were bonded together using a special water-resistant building mixture . After construction, a substantial water reservoir formed at the upstream side  of the dam. The reservoir, built in the 10th century within the Osmonsay Gorge , stretches 1.5 km in length , with a width of 52 meters  at the dam’s front and up to 200 meters  at the gorge mouth. Modern statistical analysis (Z.H. Husanxo‘jaev, research) indicates that the dam’s structural stability coefficient  is 1.80 , showing that it was designed with a special engineering plan  that even accounts for seismic risks . Construction Materials and Technological Secrets Medieval historians did not leave detailed information about the exact composition and proportions of the mixtures  used in hydraulic constructions. Perhaps for this reason, numerous legends have circulated among the local population regarding the durability of ancient monuments . For example, some sources suggest that the Kalon Minaret in Bukhara , restored in 1127 , was built using a mixture that included camel milk , while the bricks of the Alashkhan Mausoleum  in Central Kazakhstan (15th century) were reportedly made with mare’s milk . Similarly, there are claims that the Abdullakhonbandi Dam  from the 16th century incorporated camel milk and clay (shinni)  in its construction. These accounts illustrate the mysterious and advanced nature of medieval construction technology  in Central Asia, which contributed to the longevity of these structures. Structural Properties of Hydraulic Mixtures Chemical analyses of construction mixtures used in medieval hydraulic structures indicate that they possessed high hydraulic activity . As the main binding material, a combination of lime, gypsum (plaster), and special plant ashes  may have been used. Such compositions exhibit enhanced hardening under water  and resistance to erosion , ensuring that these structures retain their strength over several centuries . This demonstrates the advanced material engineering knowledge  of medieval Central Asian builders. Structure Date The percentage of construction materials Pressure in account of kg/sm 2 Relied on water Lime Plant ash Gyplsum Sand Khonbandi Dam 10 th Century             Lower slab 37 - - 63 89 155 Lower section 40 - - 60 73 54 Middle section 45 - - 55 36 56 Upper section 58 - - 42 65 65 The information quoted by A.Muhammadjonov “Quyi Zarafshon vodiysining sug‘orilish tarixi”, -Toshkent, 1972. –P.337. This table illustrates how the composition of the construction mixture varied along the height of the dam , optimizing strength, water resistance, and stability  for different structural sections. Although the structural stability  of the Khonbandi Dam was well ensured, engineers of that era were unable to devise a system to remove the silt accumulating at the bottom of the reservoir. As a result, over time, the basin gradually filled with sediment , diminishing its functional capacity. Nevertheless, the dam itself remains a remarkable example of medieval engineering and architecture , standing as a testament to the skill and ingenuity  of its builders. Conclusion and Scientific Recommendations Based on the study of the Khonbandi Dam  and similar hydraulic monuments, the following conclusions can be drawn: 1.     Engineering Genius:  10th-century irrigators were not only able to control the flow of water but also applied complex physical principles —such as hydrostatic pressure, structural stability, and seismic resistance —through mathematical calculations  in practice. The conical structure  of the Khonbandi Dam and the extraordinary thickness of its foundation  serve as clear evidence of this expertise. 2.      ·  Technological Durability:  The composition of the ancient construction mixtures  (water-resistant hydraulic mixtures) was of such high quality that it can be compared to modern concrete technologies. This ensured that the structure withstood natural forces for centuries without significant deterioration . 3.      ·  Ecological and Economic Consequences:  Since the problem of sedimentation in the reservoirs  was not addressed, over time these hydraulic systems ceased to function , leading to the desertification of the surrounding oases . This historical experience provides a valuable lesson for contemporary water management practices . Scientific Recommendations: Expand Laboratory Analyses:  The chemical composition of the mixtures used in structures such as Khonbandi  and Abdullakhonbandi should be re-examined using modern nanotechnology  to identify the natural components. This information is crucial for guiding restoration and preservation efforts . Establish a Tourist Cluster:  An open-air museum  on the theme of “Ancient Irrigation and Engineering”  could be created at the Khonbandi Dam site, which would help to enhance the tourism potential  of the Jizzakh oasis region. Digital Reconstruction:  The original state of the structure  and its water distribution mechanism  should be reconstructed using 3D modeling , allowing both the scientific community and younger generations to understand and appreciate its operational principles .   References / Bibliography 1.     Муҳаммаджонов А. “Қуйи Зарафшон водийсининг суғорилиш тарихи”, -Тошкент, 1972. –B.337. 2.     Бабаханов А. О некоторых древних водохозяйственных сооружениях Узбекистана, Известия АН УзССР, Серия общественных наук, 1959, №4, -С.45. 3.     Гулямов Я.Г. К изучению древних водных сооружений в Узбекистане, Известия АН УзССР, 1955, № 2, -С.66. 4.     Гражданкина Н.С. Из истории гидротехнического строительства в Средней Азии. –С. 113-118. 5.     Ҳусанхўжаев Э.Ҳ. Гидротехника иншоотлари, - Тошкент, “Ўқитувчи”, 1968. –Б. 10-12.   Mirzo Ulug‘bek National University of Uzbekistan, Faculty of History, Department of Archaeology and Ethnology, Associate Professor A.D. Bababekov