Walking across St Mark's Square it is hard to believe, but Venice does not stand on rock. It stands on an upside-down forest: millions of wooden piles driven into the lagoon floor.
The trick with the piles
The Venetians drove piles of alder, oak and larch, packed side by side, until they reached a layer of compact clay called caranto. On that platform they laid timber planks and then blocks of Istrian stone, which waterproofed the base and kept the walls clear of salt water.
Wood buried in oxygen-free mud does not rot: over time it mineralises and becomes as hard as stone. That is why buildings from five hundred years ago are still standing.
Numbers that tell a story
Tradition says the Rialto Bridge rests on about twelve thousand piles and that the great basilica of the Salute has more than a million. Take the figures with a pinch of salt, but they give an idea of the work and timber involved: whole forests of the hinterland were felled to build the city, and the Republic regulated the use of woodland very strictly.
And today?
The problem is not the piles but the rising water. Sea levels are rising, the ground has sunk and "acqua alta" has become an everyday issue. Since 2020 the MOSE mobile barriers have protected the lagoon from the highest tides, but they are only part of the answer: looking after a city like this takes constant care.
Next time you walk down an alley, remember there is a forest beneath your feet. On the St Mark's and Rialto tour we talk about it while looking at façades and foundations, with a few more stories.