What special construction was used in building venice?

Hello!  I am happy to help you.  Here is what I found.

"The buildings of Venice are constructed on closely spaced wood piles, which were imported from the mainland. (Under water, in the absence of oxygen, wood does not decay. It is petrified as a result of the constant flow of mineral-rich water around and through it, so that it becomes a stone-like structure.) The piles penetrate a softer layer of sand and mud until they reach the much harder layer of compressed clay. Wood for piles was cut in the most western part of today's Slovenia, resulting in the barren land in a region today called Kras, and in two regions of Croatia, Lika and Gorski kotar (resulting in the barren slopes of Velebit). Most of these piles are still intact after centuries of submersion. The foundations rest on the piles, and buildings of brick or stone sit above these footings. The buildings are often threatened by flood tides pushing in from the Adriatic between autumn and early spring."

Hope this helps!

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