Venice is a forest standing on its head. Beneath the marble façades and brick bell-towers, the city rests on millions of wooden piles — trunks of alder, oak, larch and pine — driven through soft lagoon mud into the firmer clay and sand beneath, most of them many centuries ago. The church of Santa Maria della Salute alone is traditionally said to stand on over a million of them; the figure, repeated since the seventeenth century, is suspiciously precise, but the order of magnitude is about right. The trick is that the wood never rots. Sealed in oxygen-poor mud, beyond the reach of the fungi and shipworms that destroy timber in air and open water, the piles have instead hardened over the centuries. Venice floats on drowned trees.
The city they support spreads across 118 islets, threaded by around 150 canals and stitched together by roughly 400 bridges. Legend says it was founded in a single flight of refugees fleeing Attila the Hun; the record shows a slower drift of mainlanders into the lagoon between the fifth and seventh centuries, as successive invasions made the marshes' inaccessibility look like a virtue. From that refuge grew a maritime republic that lasted some eleven hundred years, until Napoleon extinguished it in 1797. Its fabric has always been provisional: in July 1902 the great campanile of St Mark's collapsed into the piazza in a heap of rubble — killing no one, the traditional account insists, except the caretaker's cat — and the city rebuilt it com'era, dov'era: as it was, where it was.
Acqua alta
The lagoon that protected Venice also besieges it. Acqua alta — high water — is the flooding that comes when spring tides, low pressure and the sirocco wind pile Adriatic water into the lagoon, mostly between autumn and early spring. St Mark's Square, the lowest great public space in the city, goes under first — a tide of little more than a metre is enough to put water in the piazza, and at 140 centimetres roughly half the historic city is awash. Sirens with rising musical tones warn residents how high the water is expected to reach. The benchmark disaster came on 4 November 1966, when the tide peaked at 194 centimetres above the official datum and stood for hours, wrecking ground floors, workshops and archives across the city — the same day that floodwaters were destroying manuscripts in Florence. November 2019 brought the second-worst level on record, 187 centimetres, which flooded the crypt of St Mark's Basilica.
The floods worsened because the city spent the twentieth century getting lower. Industry at Porto Marghera, on the mainland rim of the lagoon, pumped groundwater from the aquifers beneath, and Venice subsided measurably until the extraction was halted in the 1970s. Add the natural compaction of lagoon sediments and the slow rise of the Adriatic, and Venice lost roughly 23 centimetres relative to the sea over the twentieth century — which is why floods that were rare curiosities in 1900 had become almost routine by 2000.
Moses at the inlets
The answer, decades in the making, is MOSE — officially the Modulo Sperimentale Elettromeccanico, a name contrived so that its acronym would echo Mosè, Italian for Moses, the prophet who parted the waters. It consists of 78 mobile steel gates lying flat in housings on the seabed across the lagoon's three inlets, at Lido, Malamocco and Chioggia. When a dangerous tide is forecast, compressed air forces the water out of the hollow gates and they swing up to seal the lagoon off from the Adriatic. Construction began in 2003 and became a byword for public-works dysfunction — costs running into billions of euros, year after year of delay, and a 2014 corruption scandal that brought down Venice's mayor. Then, on 3 October 2020, the barriers were raised against a real tide for the first time: a surge forecast at around 130 centimetres arrived, and St Mark's Square stayed dry.
Venetians know better than to declare victory. The barriers have been raised many times in the flood seasons since, and they defend against tides, not against the century-scale rise of the sea itself; every closure strains machinery sitting in corrosive salt water. But then Venice has never beaten the sea — only negotiated with it. The city on drowned trees has simply added one more clause to a truce that has held, so far, for some fifteen hundred years.
Quiz nuggets
- Venice stands on millions of wooden piles, preserved from rot by the oxygen-poor mud of the lagoon.
- The record acqua alta of 194 centimetres struck on 4 November 1966 — the same day as the great flood of Florence.
- The historic city spreads across 118 islets, linked by roughly 400 bridges.
- MOSE's 78 mobile gates guard the lagoon's three inlets: Lido, Malamocco and Chioggia.
- The MOSE barriers were first raised against a real tide on 3 October 2020; the acronym deliberately echoes Mosè, Italian for Moses.