Discover Iran: Qazvin’s underground water cisterns stand as monuments to ancient Iranian engineering

By Ivan Kesic

• Qazvin once had a remarkably dense network of over one hundred ab anbars, though only a small number survive intact today, including the Sardar-e Bozorg, which is considered Iran's largest preserved single-domed ab anbar.
• The remarkable durability of these structures depended on a specialized waterproof mortar known as saruj, whose ingredients included sand, clay, lime, ash, goat hair, and egg white.
• A computational study of four Qazvin ab anbars found that low-rise domes absorbed significantly more solar radiation than taller domes and were thermally more suitable for a relatively cold climate, demonstrating that the geometry of the dome was not merely an aesthetic choice but an important component of the cistern's environmental performance.

Beneath the bustling streets and historic bazaars of Qazvin lies one of the most remarkable achievements of traditional Iranian engineering – a vast network of underground water reservoirs known as ab anbars.

Their monumental domes once dotted the city skyline, while their sophisticated construction techniques continue to inspire architects and engineers centuries after they were built.

For centuries, Qazvin depended on these ingenious structures – roofed, underground cisterns designed to collect, store, and protect water through the dry seasons.

That was long before modern piped-water systems transformed Iranian cities. These ab anbars embodied generations of accumulated knowledge in hydraulic engineering, structural mechanics, materials science, and environmental design.

Qazvin is particularly significant to the study of ab anbars because the city once had a remarkably dense network of them. Historical accounts suggest that their number once approached or exceeded one hundred, although only a small number survive intact today.

Among the best-known are the Sardar-e Bozorg, Sardar-e Kuchak, Haj Kazem, Hakim, Jameh Mosque, and Zabaneh Bazaar cisterns.

Their distribution across the historic city reflects a decentralized approach to water supply. Rather than relying on a single monumental reservoir, Qazvin’s water-storage infrastructure was woven into the fabric of everyday urban life, serving neighborhoods, bazaars, religious complexes, and other important public spaces.

Some were built beside mosques, others formed part of larger architectural complexes, while many served densely populated residential quarters.

Underground architecture of water storage

The technical core of an ab anbar was its storage reservoir, normally constructed below ground and covered by a substantial brick vault or dome.

The underground location provided several advantages simultaneously: it protected the water from direct solar radiation, reduced exposure to extreme outdoor temperatures, and allowed the massive surrounding soil to contribute to thermal stability.

The cisterns did not exist in isolation: many were integrated into wider hydraulic systems, including qanats and channels that conveyed water into the underground reservoirs.

The form of the cistern varied according to local conditions and architectural requirements. Qazvin examples include both circular and square plans, demonstrating that there was no single universal solution.

Their measured examples included domes approximately 7.5 to 9 meters high and 9 to 14 meters wide, while computer models used standardized openings to compare the thermal behavior of different forms.

One of the most remarkable examples is Sardar-e Bozorg, whose enormous square cistern is covered by a single monumental dome and is generally described as Iran's largest single-domed ab anbar, although it is actually the largest preserved ab anbar.

Sardar-e Kuchak presents a contrasting structural solution: its reservoir is divided by a massive central column into four adjoining compartments, each capable of being separately covered.

Such arrangements reveal the structural problem facing the builders. Covering a large rectangular or square water tank with masonry without relying upon modern steel or reinforced concrete required careful control of loads, thrusts, and geometry.

The dome transformed the weight of the roof into predominantly compressive forces carried through the masonry toward the supporting walls. Brick was particularly well suited to this system because relatively small units could be arranged into curved surfaces without requiring large stone elements.

The result was a structure that combined enormous storage capacity with a roof capable of spanning large spaces using materials and techniques available to traditional Iranian builders.

Saruj, brick, and the technology of waterproofing

The remarkable durability of Qazvin's ab anbars depended on the interaction of masonry, waterproofing, and subterranean construction.

Brick was the dominant structural material, particularly for the vaults and domes, while a traditional waterproof mortar known as saruj was used extensively in ab anbar construction.

The specialized mortar had ingredients that included sand, clay, lime, ash, goat hair, and egg white, with proportions adjusted according to location and climatic conditions.

The importance of this material becomes clearer when one considers the environment in which it had to operate. The walls of a water cistern were subjected not only to moisture but also to substantial hydrostatic pressure from the stored water and lateral pressure from the surrounding earth.

At the same time, the structure had to remain stable over decades or centuries while being periodically cleaned and maintained.

Some surviving Qazvin cisterns have exceptionally massive walls: the walls of Sardar-e Bozorg are reported at approximately three meters thick, while the Jameh Mosque Ab Anbar has walls around 2.4 meters thick in some descriptions.

These dimensions should not be understood simply as evidence of primitive construction. They represent a deliberate structural strategy in which mass itself contributes to stability, durability, and thermal inertia.

The water-retaining surfaces were protected by waterproof mortar, while the heavy masonry separated the stored water from the rapidly changing external environment.

The choice of brick also offered an aesthetic advantage. Because the same material could serve structural and decorative purposes, Qazvin's builders could turn functional infrastructure into architecture.

Entrance portals, domes, brick patterns, tilework, and inscriptions could give an otherwise utilitarian water facility a civic and sometimes monumental character.

Dome as an environmental system

Perhaps the most fascinating aspect of Qazvin's ab anbars is that the apparently simple dome can be understood as part of a passive environmental system, as demonstrated by a quantitative study of four Qazvin examples.

Rather than assuming that traditional forms were environmentally efficient, the researchers tested them using ten years of meteorological data from Qazvin, modelling four different ab anbar domes, and calculating solar radiation on the dome surfaces at different times of the hottest day.

They subsequently used computational fluid-dynamics analysis to examine airflow and heat distribution inside high-rise and low-rise dome forms.

Their results produced a counterintuitive conclusion. Low-rise domes received more solar radiation than high-rise domes because of their greater exposed surface area.

In their comparison, the low-rise Sardar-e Kuchak dome was approximately 84.3 percent exposed to solar heat at 14:00, compared with 52.5 percent for the high-rise dome beside the Jameh Mosque.

At 16:00, the corresponding values were 74.7 and 53.5 percent, while at 18:00 they were 62.4 and 43.2 percent. At first glance, greater solar exposure might appear disadvantageous for a water reservoir.

But Qazvin's climate is relatively cold compared with the classic hot-arid environments where ab anbars are often discussed.

In this climatic context, the researchers found that the low-rise dome could retain more heat, while the high-rise form generated a stronger vortex of warm air near its upper region.

Their simulations therefore supported the conclusion that low-rise domes were the more suitable form for ab anbars in Qazvin's relatively cold continental climate.

The finding is important because it demonstrates that traditional architectural forms should not automatically be interpreted through the environmental logic of another region.

Qazvin's builders were working with a particular combination of winter cold, summer heat, solar exposure, and underground thermal mass. The dome was not merely a symbolic roof: its geometry affected the thermal behavior of the reservoir beneath it.

Water, air, and the logic of passive cooling

The relationship between the cistern and the atmosphere was equally important. Some Iranian ab anbars incorporated windcatchers, which could introduce moving air into the structure and help regulate temperature and humidity.

Windcatchers were added to ab anbars in some regions to keep stored water cool during summer, although their presence and configuration varied according to location.

Qazvin's surviving cisterns illustrate this diversity particularly well. Sardar-e Kuchak is described as having four domes and four semi-windcatchers, while the Haj Kazem cistern incorporated two tall windcatchers.

The Zabaneh Bazaar Ab Anbar represents another elaborate arrangement, with multiple roof elements and five windcatchers according to architectural descriptions.

The underlying principle was straightforward: water quality depends partly on the environmental conditions surrounding it. Stagnant, warm, and humid air could contribute to deterioration, whereas controlled air movement could assist ventilation and temperature regulation.

The combination of an underground tank, heavy masonry, vaulted enclosure, and, where appropriate, windcatchers therefore created a passive system requiring no mechanical refrigeration or powered ventilation.

Fresh air entering through the windcatchers promoted air circulation and could contribute to keeping the reservoir environment cooler, while the underground location and thick walls insulated the stored water from external temperature fluctuations.

The builders were not optimizing buildings according to contemporary energy-performance standards; they were solving practical problems using available materials, experience, and local climatic knowledge.

Modern simulation nevertheless allows us to see that some of these traditional solutions had measurable environmental consequences.

From infrastructure to urban monument

What makes Qazvin's ab anbars particularly remarkable is that their engineering function did not prevent them from becoming architectural landmarks and expressions of civic identity.

The practical infrastructure of water collection and storage was placed within a highly developed visual language of Iranian architecture.

A reservoir could have been little more than an underground tank, yet its entrance might be marked by a monumental portal, reached by a long staircase descending toward the water level, while the dome transformed the hidden storage chamber into a visible feature of the urban skyline.

The Sardar-e Bozorg and Sardar-e Kuchak, constructed during the reign of Fath-Ali Shah Qajar by the Sardar brothers, demonstrate how water infrastructure could become part of a larger philanthropic and architectural program.

Sardar-e Bozorg was completed in 1812 and Sardar-e Kuchak in 1814, and both formed part of the same broader complex of religious and civic construction associated with their patrons.

Other Qazvin cisterns likewise incorporated decorative entrances, tilework, inscriptions, and carefully articulated brick architecture. Their position within bazaars, neighborhoods, and religious complexes also meant that they were social spaces rather than isolated engineering works.

People descended their stairways to obtain water, gathered around their entrances, and interacted with them as recognizable landmarks of their neighborhoods.

The visual contrast between the monumental structure above ground and the immense volume of water concealed below ground is particularly striking.

What appears from the street to be a modest domed building may conceal hundreds or thousands of cubic meters of stored water.

Sardar-e Bozorg is the most dramatic example in Qazvin: its enormous underground reservoir of approximately 4,900 cubic meters and monumental dome demonstrate how Qazvin's architects transformed a fundamentally invisible infrastructure into a conspicuous urban monument.

Legacy of climate-adapted engineering

Qazvin's surviving ab anbars ultimately offer a valuable lesson in how traditional architecture can combine hydraulic engineering, structural mechanics, materials science, and environmental design within a single building type.

Their underground reservoirs exploited the thermal stability of the earth; massive masonry provided structural resistance and thermal inertia; saruj created water-resistant surfaces; brick vaults and domes allowed large spaces to be covered without modern structural materials; and windcatchers, where incorporated, could introduce passive ventilation.

The geometry of the dome itself influenced the amount of solar radiation received and the movement of warm air within the structure, as demonstrated by the recent computational study of four Qazvin examples.

At the same time, these buildings demonstrate that functional infrastructure need not be architecturally anonymous.

Their domes, portals, brickwork, tile decoration, and inscriptions gave water storage a visible presence within the city and transformed an essential public service into an element of urban identity.

Qazvin's ab anbars are therefore significant not simply because they are old or picturesque, but because they embody an integrated approach to building in which water, climate, structure, and architecture were conceived as interconnected problems.

Modern technology now allows researchers to quantify some of the performance characteristics that traditional builders could only have understood through observation and accumulated experience.

The resulting picture is neither that of a primitive technology nor of a perfectly optimized system: different forms performed differently, and the appropriate solution depended upon climate, scale, and local conditions.

That qualification makes the achievement more interesting, not less. Qazvin's ab anbars represent a tradition of empirical architectural experimentation in which centuries of accumulated knowledge produced structures capable of storing vital resources while simultaneously responding to the environmental conditions of the city.

Giant ab anbars of Iran: Qazvin and beyond

While Qazvin's Sardar-e Bozorg cistern is often celebrated as Iran's largest, two much larger cisterns in southern Iran surpass it in capacity.

The Sardar-e Bozorg Ab Anbar in Qazvin has a square tank with a volume of approximately 4,900 cubic meters, followed by the city cisterns of Jameh Mosque (3,750), Nabi Mosque (3,600), Sardar-e Kuchak (2,090), Haj Kazem (1,950), and Hakim (1,944).

However, the Kal Ab Anbar, also known as the Ganj al-Bahr Ab Anbar, in the town of Gerash in Fars Province, has a cylindrical reservoir with a diameter of 29 meters and a depth of 21 meters, storing a volume equal to 13,872 cubic meters of water, nearly three times larger than the Sardar-e Bozorg.

The Darya Dowlat Ab Anbar in Bandar Kong, Hormozgan Province, represents another remarkable achievement, with a cylindrical tank of 28 meters in diameter and 14 meters in depth, giving it a capacity of 8,620 cubic meters.

All three were built during the Qajar period, demonstrating the continued importance of traditional water infrastructure even as Iran entered the modern era.

The dome of Sardar-e Bozorg Ab Anbar, although of impressive size, with a diameter of 17 m comparable to the domes of major Iranian congregational (jameh) mosques such as the ones in Qazvin and Yazd, is nevertheless considerably smaller than the former dome of Kal Ab Anbar in Gerash.

With an astonishing external diameter of 31.5 meters and an internal diameter of 29 meters, the dome of Kal cistern surpassed even the famous Soltaniyeh Dome, which has an internal diameter of 25.5 meters and is often considered the largest historical dome in Iran.

At the time of its construction, the dome of the Kal Ab Anbar was the third largest masonry dome in the world, exceeded only by the Hagia Sophia in Istanbul and the Florence Cathedral.

What makes this achievement even more remarkable is that the Soltaniyeh Dome and the Florence Cathedral were built by the best engineers of their time with generous financing from emperors and the ultra-wealthy Medici family, while the Kal Ab Anbar was built by residents of a peripheral town that then had a population of a few thousand.

Although the brick dome did not survive the devastating earthquake that struck Fars Province at the beginning of the twentieth century, the cylindrical structure has been preserved to this day, and the ab anbar continued to be used for many decades until the introduction of a modern water network.

These southern Iranian ab anbars, though less well-known than their Qazvin counterparts, represent some of the most extraordinary achievements of traditional Iranian engineering and deserve recognition alongside the more famous cisterns of central and northern Iran.

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