Mud, water and wood: The system that kept a 1604-year-old city afloat

Venice is a remarkable city that has been thriving for over 1,600 years, and its unique construction methods have allowed it to remain afloat in the water. The city is built on a foundation of millions of wooden piles, which are essentially tree trunks that have been driven deep into the ground. These piles are made from various types of trees, including larch, oak, and pine, and they have been supporting the heavy stone buildings for centuries. Unlike modern buildings that are typically constructed with concrete and steel, which are designed to last around 50 years, the wooden piles of Venice have proven to be incredibly durable. Alexander Puzrin, a professor of geomechanics, pointed out that while concrete and steel are strong materials, they do not have the longevity of the wooden piles found in Venice. He recounted an experience early in his career when he was asked to guarantee that a building would last for 500 years, which is quite unusual in the construction industry. He was initially taken aback but ultimately decided to sign the guarantee, knowing that no one would be around to verify it. The technique used to place the wooden piles is fascinating and complex. While no one knows the exact number of piles beneath the city, it is estimated that there are millions. For instance, under the San Marco Basilica, there are approximately 10,000 oak trees that were used to create a solid foundation. Caterina Francesca Izzo, a professor at the University of Venice, shared her insights about the wooden piles. Growing up in Venice, she was aware of the trees beneath the buildings but did not fully understand how the piles were installed or the significance of the workers known as battipali, or pile hitters. These workers would manually hammer the piles into the ground while singing traditional songs to maintain a rhythm. The songs often celebrated Venice's history and its glory. The process of driving the piles involved starting at the outer edge of the structure and working towards the center, with multiple piles placed in a small area to create a strong base. After the piles were driven in, wooden boards were laid on top to support the buildings. The Republic of Venice recognized the importance of preserving its forests to ensure a steady supply of wood for construction. This practice, known as sylviculture, was essential for maintaining the city's infrastructure. Nicola Macchioni, a research director, explained that the rules for sustainable wood use were established as early as 1111 AD in the Fiemme Valley, which is located northwest of Venice. These conservation practices likely existed long before they were documented, allowing the forests to thrive even today. While Venice is not the only city that relies on wooden piles for its foundations, it is unique in its approach. Cities like Amsterdam also use wooden piles, but they extend down to the bedrock, functioning like columns. In contrast, the piles in Venice do not reach the bedrock, relying instead on friction between the wood and the soil to support the buildings. This innovative method of construction has a long history, with references dating back to the Roman Empire, where submerged piles were used for bridges. The Aztecs in Mexico City also employed similar techniques until their city was destroyed. Despite the impressive resilience of Venice's foundations, they are not without challenges. A research team from the universities of Padova and Venice conducted a study on the condition of the city's foundations. They discovered that some of the wooden piles were deteriorating due to the action of anaerobic bacteria. However, the combination of wood, water, and mud continues to hold the structures together. The researchers found that the wood does not rot in the absence of oxygen, and the water helps maintain the shape of the wood. Even if some piles are damaged, the overall system remains intact. Caterina Izzo emphasized the importance of ongoing research to monitor the foundations, as it is unclear how many more years they will last. The longevity of the foundations depends on the stability of the environment. The soil, water, and wood all work together to create a strong foundation. In recent years, there has been a renewed interest in building with wood due to its environmental benefits. Wood is a sustainable material that can help reduce carbon emissions. While it may not be feasible to construct entire cities from wood today, the ancient builders of Venice demonstrated remarkable ingenuity in their use of natural materials, creating a city that has stood the test of time.