I. Introduction

Venice, the Floating City, is a marvel of human ingenuity. Rising out of the Adriatic Sea, the city is nothing short of an engineering miracle that has captivated historians and engineers to the present time. For a city that is all on water, with one of the main modes of transportation being by boat, one may start to wonder, how did this place come into existence? Its winding canals, palaces, intricate bridges, and resilience in surviving the odds in a water landscape have become a statement of human engineering and creativity. The story of Venice’s creation is one of adaptation, determination, and a mastery of both nature and technology.

The origins of Venice trace back to a time of instability in Europe, a time when the collapse of the Roman Empire due to barbarian invasions left the continent in a state of chaos. As these barbarian tribes swept across Europe, the inhabitants of the mainland fled to the Venetian Lagoon. At the time, the lagoon only contained a series of marshy islands that would seem inhospitable as each island could barely even support the weight of a human body. If you stepped onto the islands, you would sink to about your waist. The environment was a different story as well. Shifting sands, constant flooding, and the lack of fresh water are the challenges that had to be taken into consideration to build this city (Cunningham, 2024).

The refugees who sought safety in the lagoon were driven by the necessity to create a new kind of settlement that could survive in such an environment. What began as a series of stilt houses gradually evolved into a more sophisticated urban center as the settlers harnessed the elements that threatened them. They drove wooden piles deep into the soft, muddy ground, creating a stable foundation to build their homes and public buildings. Over time, these structures gave way to a network of canals and streets as the settlers learned to control the flow of water, turning their greatest obstacle into an asset that became crucial (Cunningham, 2024).

The construction of Venice was not just a feat of engineering but also a testament to the power of human collaboration. The early Venetians understood that their survival depended on the balance between the forces of nature and the needs of their growing community. This understanding led to the development of a unique approach to urban planning and architecture, one that used the natural environment rather than sought to dominate it. The city’s layout, with its labyrinthine canals and narrow streets, reflects a deep respect for the lagoon’s unpredictable tides and shifting sands.

As we delve deeper into the history and mechanics of Venice’s foundations and the structural supports of buildings, we uncover not just the technical aspects required to build a city on water but also the vision and determination that transformed this dream into a reality. This article explores the construction techniques that enabled Venice to be built on the unstable, waterlogged terrain of the Venetian Lagoon, including the materials used, such as wood, brick, and stone, and how they contribute to the city’s stability. It also examines the modern preservation efforts, including the MOSE project, aimed at protecting Venice from rising sea levels and subsidence.

II. The Creation

Background

Origins and Early Settlements

Venice’s story begins in the 5th and 6th centuries AD. As the Roman Empire declined, barbarian invasions prompted the local inhabitants to seek refuge on the marshy islands of the Venetian Lagoon. These islands offered natural protection due to their water-surrounded location and challenging land access (All About Venice , 2024).

Initially, settlers constructed structures mainly made from wood, reed, and clay. These houses were lightweight, and the sandbanks were enough to sustain them. However, these early buildings were unstable and susceptible to environmental damage, being flooded nearly twice a day. Recognizing the need for more robust foundations, the Venetians innovated their construction methods to suit their environment better (All About Venice , 2024).

The Piles

Here, we will start at the very first layer of the foundations. The construction challenges posed by the Venetian Lagoon’s soft, marshy soil, which lacked load-bearing capacity, led the Venetians to develop this solution: wooden piles.

Foundation Techniques and Waterlogged Conditions
The Venetians collected large timber piles from the forests of Croatia and drove them deep into the islands of the lagoon. These piles had varying diameters from 10 to 25 cm and heights from less than 1 m to a maximum of 3.5 m, with around nine piles driven into the ground per square meter. Oak, pine, alder, larch, and elm were the primary woods used for these piles due to their durability and resistance to decay (Capretti et al., 2016).

The enduring nature of Venice’s wooden foundations led to the belief that wood buried in mud remains preserved. This is due to the lagoon’s unique chemical, physical, and biological conditions, which hinder rapid decay. The environment prevents most biological factors from affecting the wood, allowing it to remain intact and even harden to a stone-like state over centuries (Capretti et al., 2016). The lagoon’s waterlogged environment plays an important role in preserving and mineralizing the wooden piles. Wood exposed to air or dry conditions is typically prone to decomposition by fungi and bacteria. However, the constant saturation with saltwater and the oxygen-poor conditions of the lagoon inhibit these microorganisms, drastically slowing the decomposition process. The waterlogged conditions act as a natural preservative, preventing the piles from drying out and cracking (Baker, 1969). The movement of the tides also helps keep the piles waterlogged, preventing exposure to air that could lead to their drying and deterioration. (Freitag et al., 1996). Understanding how the lagoon’s conditions contributed to this transformation demonstrates the ingenuity behind Venice’s construction techniques.

Furthermore, the lagoon’s mineral-rich environment, particularly calcium carbonate, contributes to the mineralization process. Over time, these minerals infiltrate the wood’s porous structure, filling holes left by decaying material and solidifying the wood into a more rigid, stone-like substance. This process, though not true petrification, enhances the structural integrity of the piles, enabling them to support Venice’s buildings for centuries (Fossils, n.d.). Today, these piles have effectively become as hard as stone beneath the city.

Clay and Mud Layers
In addition to the mineralization process, the lagoon’s thick layers of clay and mud also play a vital role in preserving the piles. When the wooden piles were driven into the lagoon floor, they penetrated soft clay layers, adding another protective element. The mud and clay in the Venetian Lagoon are composed primarily of fine particles of silt, clay, and organic matter, which have been deposited over thousands of years by the natural flow of rivers into the lagoon. The Po, Piave, and Adige Rivers all contribute sediment to the lagoon, bringing with them minerals and organic materials from the surrounding mountains and plains. Over time, these materials settled at the bottom of the lagoon, creating thick layers of mud and clay that make up the foundation upon which Venice was built (Bellucci et al., 2001).

Clay’s Role in Foundation Stability
The clay’s fine particles have a dense and cohesive structure, making it resistant to erosion and compaction despite being waterlogged. This density allows the clay to support the weight of the wooden piles and stone foundations without shifting. The clay also acts as a barrier, sealing the wood from oxygen exposure and isolating it from elements that cause decay. The waterlogged conditions keep the mud and clay soft yet stable, preventing soil erosion and ensuring the piles remain firmly anchored to support Venice’s structures (Bellucci et al., 2001). Though Venice’s foundations rest on mud and clay, these layers have provided a stable base for centuries due to the natural properties of the sediment. The dense clay locks the wooden piles in place, preventing the buildings from sinking or tilting (Cunningham, 2024). The cohesive nature of the clay also protects against erosion from the lagoon’s water movements. This resistance helps maintain the stability of Venice’s foundations over time (Bellucci et al., 2001). Understanding the role of Venice’s mud and clay layers can help us appreciate the engineering aspect that has allowed this city to thrive for over a millennium.

The Materials

Moving up the layers of Venice’s foundations, we approach the second layer, the stone, brick, and mortar. These materials play a critical role in the stability of Venice’s foundations. The city’s unique construction method, combining wooden piles with stone and brick, provided the necessary support for its buildings on soft, waterlogged terrain.

Transition to Stone and Brick
One of the key components that contributed to the longevity and stability of Venice is its use of stone and brick in the foundations of its buildings. These materials, used in combination with wooden piles, provided the support needed to build the city atop its watery terrain.

Once the piles were driven into the ground, they were capped with wooden planks or stones to be able to build the foundations that would support the weight of Venice’s buildings. This method allowed structures to be supported above the unstable topsoil. However, as Venice expanded, more durable materials became necessary. Stone and brick were increasingly used for building foundations. Local limestone and marble were also available to them. The combination of stone and wooden piles led to the development of more long-lasting structures (Venezia Autentica, 2023).

Brick in Venetian Foundations

Bricks played an essential role in the construction of Venice’s foundations. Venetian bricks, known as mattoni, were typically made from clay, which was abundant in the nearby regions of the Venetian Republic. These bricks were small, uniform in size, and easy to handle, making them ideal for the precision needed in foundation work.  

Four Important Properties of Brick in Foundations

1. Water Resistance: One of the most important features of Venetian brick is its water resistance. Properly fired bricks become almost impermeable to moisture, which is critical for buildings in a lagoon environment. Then, a vitreous surface was applied to enhance the mechanical strength and make the bricks suitable for underwater foundations, making them resistant to saltwater. Venetian bricks were fired at high temperatures, making them strong and highly resistant to water. In Venice, where the ground is often saturated with water and buildings are exposed to high tides and flooding, bricks provide a reliable material that can withstand constant exposure to moisture without deteriorating extremely quickly (Bison et al., 2023).
2. Strength and Durability: Brick also has impressive load-bearing capabilities, making it an excellent material for building foundations. The uniform size and shape of Venetian bricks allowed for precise construction, ensuring that the building’s weight was distributed evenly across the foundation. This was particularly important in Venice, where the soft ground required a stable and consistent base (BKreative, 2017).
3. Thermal Insulation: While its use in foundations is primarily structural, brick also offers the benefit of thermal insulation (Bison et al., 2023). The dense material of brick helps regulate temperature within buildings, keeping them cool in summer and warm in winter. This insulation was particularly important in Venice’s humid climate, where temperature control would have been a significant concern (BKreative, 2017).
4. Adaptability: Venetian bricks were relatively small, allowing builders to use them in various settings, including irregular or uneven surfaces. This adaptability made bricks an ideal material for constructing foundations in the shifting terrain of the lagoon, where flexibility was necessary to ensure stability (BKreative, 2017).

The Use of Stone in Venetian Foundations
Alongside brick, stone was another crucial material used in the foundations of Venetian buildings. Stone provided the strength and durability needed to support large, heavy structures. Two primary types of stone were used in Venetian foundations: Istrian stone and limestone.

Istrian Stone
Istrian stone is a reef limestone of a sedimentary nature characterized by gray-green or white shades. The dense limestone quarried from the Istrian Peninsula (now part of Croatia) was one of Venice’s most important building materials. It was highly prized for its water-resistant properties, strength, and aesthetic appeal. Istrian stone was often used at the lower levels of buildings, where the structure was in direct contact with water (Bison et al., 2023).

1. Water Resistance: Istrian stone’s natural resistance to water made it an ideal material for the foundations of Venetian buildings. Unlike many other types of stone that absorb moisture and erode over time, Istrian stone has low porosity, is resistant to salt erosion, and has a high resistance to a water environment. This quality allowed it to withstand constant exposure to water without becoming porous or crumbling, an essential feature in a city where high tides regularly flood the lower parts of buildings (Bison et al., 2023).
2. Strength and Load-Bearing Capacity: Istrian stone’s dense composition also made it highly durable and capable of supporting heavy loads. This was necessary in Venice, where many buildings were constructed from heavy materials like brick and marble. By using Istrian stone in the foundations, builders could ensure that the structure would be stable and capable of bearing the weight of the upper floors (Bison et al., 2023).
3. Aesthetic and Functional Qualities: In addition to its practical benefits, Istrian stone was also valued for its aesthetic qualities. Its beautiful bright white color contrasted beautifully with the darker bricks used in Venetian architecture, giving the city its distinctive look. Over time, the stone developed a weathered patina, which, in my opinion, added charm and character to Venice’s buildings.

Limestone
While Istrian stone was used for the most critical parts of Venetian foundations, limestone was also employed in certain areas. Limestone is a softer, more porous stone than Istrian stone, but it was more abundant and easier to work with. It was often used in the upper portions of foundations, where it was less likely to be exposed to water (Babanina et al., 2019).

1. Cost-Effective: : Limestone was more readily available and less expensive than Istrian stone, making it a great choice for large-scale construction. Its affordability allowed builders to use it in areas with less intense structural demands, such as the upper levels of foundations and non-load-bearing walls (Babanina et al., 2019).
2. Ease of Shaping: Limestone is softer than Istrian stone, making it easier to cut and shape. This quality allowed for greater flexibility in the design of foundations and made it a popular choice for intricate architectural details (Babanina et al., 2019).
3. Porosity and Limitations: Limestone’s porosity made it less suitable for water-exposed areas. For this reason, it was generally used in parts of the foundation above the waterline, where its tendency to absorb moisture would not cause structural problems (Babanina et al., 2019).

Pozzolana Mortar: The Binding Agent

A key component of Venetian foundations, in addition to brick and stone, was the mortar used to bind these materials together. The Venetians used a type of hydraulic binder made from pozzolana, a volcanic ash imported from the regions around Mount Vesuvius. The Pozzolana mortar was highly prized for its ability to set and harden underwater, making it ideal for the wet conditions of Venice (Singh, 2023).

1. Waterproof Properties: Pozzolana mortar can harden even when submerged in water, making it perfect for use in the foundations of Venetian buildings. This property was crucial in a city where the lower parts of buildings were often in contact with water (Singh, 2023).
2. Strength and Flexibility: Pozzolana mortar creates a strong and durable bond between bricks and stones, adding to the overall stability of the foundation. It also has a degree of flexibility, which allows it to absorb small movements in the foundation without cracking. This was particularly important in Venice, where the soft, shifting ground of the lagoon required a foundation material that could adapt to changing conditions (Singh, 2023).

The Combination of Stone, Brick, and Wood

The combination of stone, brick, and wood was key to the success of Venetian foundations. Wooden piles provided the needed support to stabilize the foundation, while brick and stone offered the strength and water resistance required to build long-lasting structures. This combination of materials allowed the Venetians to create a foundation system uniquely suited to their challenging environment. Using the resources available to them, they were able to build a city that has lasted until the present day despite the constant threat of flooding and the unstable ground beneath it.

Modern Day

Venice’s foundations face ongoing challenges from rising sea levels, subsidence, and material decay. Nevertheless, the question really is, will Venice last for a decade, a century, or more?

Is Venice really sinking?
The idea that Venice is sinking has been discussed for centuries, and while the phrase is commonly used, the reality is more complex. Venice is both sinking and facing rising sea levels. These two factors combined are causing the city to experience more frequent and severe flooding.

Venice is sinking primarily due to the natural process of the ground/hard clay slowly compacting under the weight of the city’s buildings. The city was constructed on wooden piles driven into clay. However, over time, the compaction of the soil, combined with human activity like groundwater extraction in the 20th century, has accelerated subsidence. Though groundwater extraction was halted in the 1970s, the damage had already been done, and the city continues to sink at an estimated rate of 1-2 millimeters per year (Vella, 2023).

At the same time, global sea levels are rising due to climate change, intensifying Venice’s flooding issues. The city is particularly vulnerable to acqua alta (high water) events, where tides rise unusually high and flood the city streets. These events become more frequent and severe as sea levels rise and weather patterns become more unpredictable (Keahey, 2002).

The combination of the settling sediment deep under the waters of the lagoon and rising seas means that Venice is, in effect, sinking. Still, it’s not just the city descending into the ground—it’s mainly the water levels rising around it. Efforts like the MOSE project aim to protect Venice from flooding in the short term, but long-term solutions are still uncertain. Without major intervention, experts predict that Venice could face significant challenges in staying above water by the end of the century.

MOSE
One significant project to temporarily stop Venice from sinking due to the increasing sea level is MOSE (Modulo Sperimentale Elettromeccanico). It is specifically designed to protect Venice from high tides and flooding with a series of barriers controlling water flow into the lagoon. This project highlights the ongoing commitment to preserving Venice’s architectural heritage while addressing contemporary environmental threats. It is a large-scale engineering initiative designed to protect Venice and its surrounding lagoon from the increasingly frequent high tides and storm surges. These floods, intensifying due to climate change, rising sea levels, and land subsidence, threaten Venice’s cultural heritage and the lives of its residents (MOSE Venezia, n.d.).

First conceived in the 1980s, MOSE consists of a series of mobile barriers at three key inlets—Lido, Malamocco, and Chioggia—that connect the Venetian lagoon to the Adriatic Sea. The barriers are designed to remain on the seabed during normal conditions, allowing ships and water to pass freely. However, when the tide rises beyond 110 centimeters, compressed air is injected into the hollow barriers, causing them to rise and block the water inflow from the sea, thereby protecting Venice from flooding (Water Technology, n.d.)

MOSE’s Effect on Venice’s Foundations
The MOSE project is important in protecting Venice’s foundations, which are vulnerable due to the city’s unique construction on wooden piles.  Over centuries, the rising sea levels and the frequent high tides threaten Venice’s foundations, which, if unchecked, accelerate erosion and subsidence. The MOSE project directly addresses these challenges by reducing the frequency and intensity of flooding events, therefore slowing the deterioration of the city’s structural base.

Because Venice’s buildings rest on wooden piles in clay beneath the lagoon’s waters, the wood remains well-preserved underwater due to the lack of oxygen. However, prolonged exposure to saline water from frequent flooding increases the risk of erosion and damage to the upper layers of buildings. An article about the sinking city of Venice writes, “Because the sea level has risen, even in a modest flood, the water level rises above the waterproof marble foundations of the buildings, rapidly wearing away the less-robust building materials.” So due to this abnormally high water level, it has reached the bricks, stone, and mortar that form Venice’s iconic architecture, which are highly susceptible to saltwater corrosion, leading to structural weakening over time (Kissell, 2019).

This means by deploying barriers at the lagoon’s inlets during high tide events, MOSE prevents storm surges and excessive saltwater from infiltrating the city. This reduction in water exposure helps limit the absorption of saline water into building materials, slowing the process of salt crystallization, which is a major contributor to structural decay in Venice. Fewer floods mean less direct contact with corrosive seawater for the city’s foundations and historic structures.

Additionally, by lessening the frequency of flooding, MOSE helps maintain more stable ground conditions. Continuous waterlogging can weaken the soil beneath Venice even further, leading to subsidence and uneven settlement of buildings, which has already been happening with many of the buildings. With fewer flood events, the pressure on the lagoon’s sediment is reduced, providing more stability for the city’s foundations (Kissell, 2019).

While MOSE is unfortunately not a permanent solution to Venice’s environmental and structural challenges, it offers significant short-term protection for the city’s foundations, buying time for more comprehensive preservation and adaptation strategies for the future.

Figure 12: A photo of a man wading through St. Mark’s Square, the lowest point in Venice that floods quickly due to its low elevation with the sea level

III. Summary

Venice’s creation and continued existence on its unique marshy foundations is a testament to human ingenuity. From its origins as a refuge for people fleeing barbarian invasions, the city developed into one of the most remarkable urban centers in the world, both in terms of its beauty and engineering prowess. The transformation of the Venetian Lagoon’s inhospitable marshy islands into the foundation of an entire city is remarkable, especially during that time.

Venetians faced challenges as they attempted to establish stable living conditions in a lagoon environment that was constantly shifting, waterlogged, and lacking solid ground. The solution to this problem was the innovative use of wooden piles. These piles, driven deep into the lagoon’s muddy bed, provided the necessary foundation for the city’s buildings. The Venetians utilized multiple durable wood types, which resisted decay due to the unique waterlogged conditions in the lagoon. Over time, mineralization processes further hardened these wooden piles, allowing them to support structures for centuries. Additionally, the city’s reliance on materials like brick, stone, and mortar demonstrates a careful and well-thought-out approach to construction. Bricks, particularly those made to resist saltwater, along with the highly durable Istrian stone, were essential in ensuring that Venice’s buildings could withstand the harsh conditions of the lagoon. Pozzolana mortar, with its water-resistant properties, played a critical role in binding these materials together, making the city’s foundations more resilient to the effects of constant exposure to water.

When I walked around Venice, I found that it was really fascinating that this whole city is sitting on deep, unseen foundations. The whole city was built all the same way, no matter how large the building was on top. From an engineering aspect, it was amazing that the city, built more than a thousand years ago, could even be built with the technology they had at hand. And in their situation, under the barbarians’ pressure, made this feat even more impressive.

Despite the remarkable achievements in Venice’s early history, the city faces new challenges in the modern era. Rising sea levels due to climate change, material decay, and subsidence threaten the foundations that have supported Venice for over a millennium. Projects like the MOSE barrier, designed to protect the city from high tides, are part of ongoing efforts to preserve Venice for future generations, as the MOSE barrier is simply a temporary solution. However, these challenges highlight the delicate balance that Venice has always had to maintain between its environment and its survival. Due to climate change, the increase of the rising sea levels had not been predicted a thousand years ago. It is up to the future generations of engineers to find a way to create another temporary solution or a permanent solution that can preserve this floating city for the next thousands of years.

IV. References

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