A short history of Venice and its canals

Venice is one of the most famous cities in the world, thanks to its fabled canals and stunning architecture. Beautiful monuments such as the Doge's Palace, St. Mark's Basilica, and Piazza San Marco captivate over five million tourists a year.

At first glance, Venice appears to be floating on the water and is connected by a maze of canals. These waterways are the lifeblood of both Venice's tourist industry and the city itself. Water taxis ferry citizens to and fro, while tourists flock to the ubiquitous gondola rides.

Nicknamed the “Floating City” because it stretches across the Venetian Lagoon, Venice’s construction and its continued refusal to collapse into the sea is an astounding feat of human engineering.

The founding of Venice

Marshlands were the initial grounds of Venice.
Marshlands were the initial grounds of Venice. [CC] credit.

Venice was initially built on marshlands.

The Venetian Lagoon consists of about 120 islands nestled amongst the marshes that stretch out from Italy's Adriatic Northern coast. It was here that Venice was founded in the 5th Century AD, as refugees from the collapsing Western Roman Empire fled the onslaught of barbarian hordes by sailing away from mainland Italy.

Before the arrival of Roman refugees, the islands were home to a small community of fishermen. These fishermen mainly lived in simple huts built on the islands themselves. As more refugees found themselves sheltering in the lagoon, more and more space was needed. But at first, there seemed to be nowhere to build a new settlement. The islands were flanked by marshlands and sea, and there were no forests to be cut down for building lumber.

To expand the usable land, the prospective Venetian settlers had to find a way to dredge the marshes. So they constructed a series of canals that would divert the water away and reveal more land for them to build upon. The sides of these canals were strengthened with wooden planks and stakes to prevent them from being refilled by the tides.

To start building, the settlers used more wood in the form of piles to create stilts. They did this by digging down into the marshy soil and driving in the wooden pilings. Now, they could lay wooden boards on top of the pylons to provide a foundation strong enough to start supporting stone. Thousands of supports rapidly expanded the area of Venice, and many may still be standing today.

The wood for these initial structures had to be brought over from the mainland and ferried across the sea. The vast forests of Croatia, Montenegro, and Slovenia were the main sources of lumber. With the foundations of Venice built, the city began to grow.

Venice Expands Across the Lagoon

The Venetian lagoon before the construction of Venice. The current city is outlined in black.
The Venetian lagoon before the construction of Venice. The current city is outlined in black.

The success of these wooden supports was due to their length. Many of them were up to 60 feet long. Because of their size, the Venetians were able to drive the supports deep enough to reach something unexpected; a hard layer of clay. This clay substrate was known as the caranto and was strong and thick enough to essentially hold the wooden piles in place. This enabled the supports to bear the weight of the buildings above. The caranto could be as deep as 10 meters in some areas of the lagoon.

But not all of the piles had to be buried in the caranto. The Venetians were able to bury hundreds of pylons in both the weaker soil and mud and the water itself. This allowed them to expand Venice even beyond the relative safety of the islands, and the city soon began to spread to cover virtually the entire lagoon.

The Venetian builders could tell how solid the substrate was when setting the piles because varying depths of silt or clay gave different levels of resistance. Wherever possible, several piles were packed very closely together in the looser layers to increase their collective strength. This was used especially when constructing the defensive walls of the city. In between these pylons, the Venetians dropped rocks and stones. This helped increase the strength of their foundations whilst also preventing any build-ups of silt.

Two or more layers of wooden boarding were often laid on top of the piles. This increased their strength so that they could begin to support the weight of materials such as stone and masonry. The Venetians used materials such as marble or certain types of limestone because of their impermeable properties, further protecting their buildings from the water.

Stone layers were added on top of these wooden boards underneath the water surface, providing rock-solid foundations for streets, bridges, and buildings. As the network of supports spread, the Venetians could build bigger and heavier monuments.

Laying Venice's Foundations

How Venice and its canals are built.
How Venice and its canals are built.

In the first few centuries of Venice's expansion, these piles were usually buried by hand, as the settlers didn't have access to the advanced machinery of later eras. It was back-breaking, cumbersome work, even though the lengths first used by the settlers were relatively short. These builders also could not work on solid ground until they had buried the initial supports, and so probably struggled against the boggy, marshy ground.

The earliest method involved two or more men burying the poles into the substrate through sheer manpower. They would place something heavy on the top of the pole, most likely other pieces of wood or stone, and then hammer the wooden support down into the ground. As the centuries passed, science and engineering produced more efficient mechanical methods of boring the holes for the supports.

It has been theorized that the great Leonardo Da Vinci may have invented a medieval form of pile driver during his time in Venice. This device was controlled by a winch that an operator would work by hand and could hammer the piles into the ground more quickly and efficiently.

Keeping the Supports Intact

Normally, wood rots if placed underwater for extended periods. This would've proven catastrophic for the Venetian settlers. However, to prevent this they used trees like alders, larches, and oaks that are naturally resistant to water damage.

But this alone would not have been enough. Luckily, because the wooden pilings were buried in a thick layer of clay and mud substrate, oxygen had virtually no chance to reach the wood and cause rotting. This prevented microorganisms from infiltrating the wooden supports and eating away at them.

This would normally cause decay and eventually collapse, but over hundreds of years, minerals and sediment from the mud and the saltwater seeped into the wooden pylons and gradually allowed them to petrify. Venice's foundation of wooden piles was soon as solid and strong as stone.

Venetian Grandeur Reaches its Height

From the 7th Century to the 18th Century, Venice was a republic. During that time, the city-state grew in wealth and power and experienced its peak around the 13th Century. Venice quickly became a formidable naval power and strategic trading center during the Renaissance and became one of the wealthiest cities in Europe. Venice also held control over parts of Italy and the Adriatic coast, such as Slovenia.

As Venice's riches grew thanks to her trade links with the rest of Italy and further afield, Venetian builders could construct bigger and more impressive architectural marvels. Churches and palazzos sprang up around the city. For some of these grander projects, detailed records were kept about their construction. This helps give us a clear picture of how Venice was built over the centuries.

In the 17th Century, a book gave an account of the construction of the church of Santa Maria Della Salute in the Dorsoduro district. In just over two years, more than 1.1 million wooden piles were hammered into the water to form the foundation of the church. All of these supports were around four meters long.

The foundations of Venice are made of wood pilings.
The foundations of Venice are made of wood pilings.

But even with these foundations in place, there were some issues. Due to the weight of the streets and buildings above, the marshy soils and clay layers that held the supports were slowly compacted. This meant that the foundation wasn't entirely even or level. As such, the majority of Venice's buildings do not stand straight. This is most visible when looking at bell towers or other tall structures.

Some buildings also collapsed throughout the centuries, sometimes due to the ancient supports being unable to take the weight of countless additions or changes to the structures. One of the more famous collapses was that of St. Mark's Campanile. The Campanile’s foundation had been constructed in the 10th Century from alder lumber supports that measured almost two meters long. These piles were pounded into a layer of clay five meters below the water.

St. Mark’s Campanile had survived earthquakes, fires, and lightning strikes for centuries. But during renovation work in 1902, disaster struck. The renovation work compromised the supports within the tower, and the Campanile collapsed in July. The foundation supports remained largely intact despite being thousands of years old and were shored up with over 3000 additional pilings.

The Problems Facing Modern Venice

However, despite being an incredible feat of human engineering the unique foundations of Venice have caused problems over the years. Even though the builders of Venice now have modern construction techniques and greater knowledge about the region, these problems cannot be avoided.

Throughout its history, Venice's location has made procuring safe sources of drinking water difficult. The waters that Venice floats are comprised of saltwater that originates in the Mediterranean and flows into the Adriatic.

To combat this problem in the 1960s, a series of artesian wells were constructed throughout the city. However, the drilling process required to reach the water underground began to drain water from the layer of caranto clay that supports many of the city's foundations. This caused Venice to sink alarmingly, so the project was abandoned.

Today Venice faces grave threats from its own sinking foundations and climate change. The city has always been sinking slowly. This is because the weight from Venice’s buildings has been compacting the layers of clay and silt underneath them for centuries. Flooding has long been an issue for the city, especially during high tides known as “aqua alta”.

These high water periods are the result of tumultuous weather conditions in the Adriatic, such as high winds or surging storms. November 2019 saw Venice experience its worst bout of flooding in 50 years.

But thanks to the rising sea levels associated with climate change, Venice is facing a real problem. Not only is the city itself gradually sinking, but the waters around it are rising as the polar caps melt. Some climate change scientists predict that Venice could be completely submerged by 2100. Several initiatives such as Project MoSE have been proposed to combat the crisis facing Venice.

Project MoSE in particular has been given a lot of attention. The plan consisted of building almost 80 moveable floodgates that could help control the flow of water into the Venetian Lagoon. These contraptions were placed throughout the Lagoon's three main inlets. The initiative has had a turbulent history, but the system was tested for the first time in July 2020. However, it isn't expected to be ready for another couple of years.

Venice is an enchanting city, and its foundations may be the most fascinating part of its proud history. But for all the modern advancements and initiatives, it is still a city that relies on unlikely foundations that are hundreds of years old. And that is a truly astounding fact.