The Secret of the Floating City, Venice

It turns out that refugees fleeing the barbarian invasions following the collapse of the Western Roman Empire
built floating houses by driving about a million wooden stakes into the tidal flats. Wow.
I heard they brought in timber from Northern Europe as if sweeping it all up to get those million stakes.
Since it was before the Age of Discovery, Mediterranean trade was the core, and they say it was thanks to the wealthy commercial districts.
The amazing thing is that the wooden stakes haven't rotted well for over a thousand years; they didn't necessarily know that back then,
but as they lived and adapted, it turns out the wood doesn't rot easily even after a millennium.