A remarkable city in Europe which is held aloft by a surprising combination of physics and engineering has been standing for an incredible 1,604 years. The “floating city” stands on a foundation of trees hammered into the earth.

Most people who visit Venice and enjoy floating through the canals are unlikely thinking about what is holding up the heavy stone buildings around them. But the Italian city, which is spread over 118 small islands, meant finding a way to build on unstable, waterlogged soil. Early Venetians solved the problem with creativity and took alder, oak and pine trees, and pounded them into the ground to provide a base to build on. Whilst some of these logs are over 3.5m long, some are less than a single metre.

Before this, the first attempts at construction in the city used large stone blocks to stabilise the soft shores of the islands. But the watery sand could not support the immense weight.

The timber they used was resistant to water damage and sourced from mainland Italy and south-eastern Europe. It remains anyone’s guess how many wooden poles there are in the whole of the city, but under San Marco Basilica alone, there are 10,000 oak trees.

All of the piles were driven into the ground by hand, using a combination of tools and tactics. One manually operated hammer, the “attrezzatura”, weighed over 500 pounds and had to be operated by a whole team of labourers.

Maybe most surprising is how durable this approach has proven. Driving the poles into the soil reinforces the ground by creating friction between the wood and the soil. “The beauty of it is that you’re using the fluid nature of the soil to provide resistance to hold the buildings up,” Thomas Leslie, a professor of architecture at the University of Illinois, told the BBC.

There is a common belief that because these wooden poles are underwater, they don’t rot because of the lack of oxygen. Caterina Francesa Izzo, an environmental chemistry and cultural heritage professor at the University of Venice, and her team inspected the foundations and found they were degrading.

But the good news for Venetians, and tourists alike, according to Ms Izzo who was born and raised in Venice, is that the current combination of wood, soil and water means the foundations erode at a much slower rate.

As long as nothing drastic happens, and these three elements remain intact, this feat of engineering might well stand for another 1,600 years.