Walk into the church of Santa Maria della Salute on the southern tip of Venice's main island cluster, take off your shoes, and you would find — if the floor were stripped back — that the entire massive baroque structure rests on something extraordinary: roughly 1.1 million wooden pilings, hammered into the lagoon mud over the course of a century, supporting the marble facade above them. The pilings are not stone. They are tree trunks of oak, larch, and alder, harvested mostly from the forests of the Alpine foothills and floated down to Venice on rafts. They have been submerged in oxygen-poor lagoon mud for nearly 400 years. They have not rotted. They have actually become harder and more durable than when they were first installed, because the lack of oxygen prevents the wood-decay fungi from operating, and the dissolved minerals in the lagoon water have gradually mineralised the wood from the outside in. The pilings are the foundation of the foundation of Venice, and one of the few engineering bets in human history that has paid off more handsomely than its designers can possibly have expected.
Why Anyone Built a City Here
Venice exists because in the 5th and 6th centuries CE, refugees fleeing the collapse of the Western Roman Empire and the subsequent waves of Germanic and Hunnic invasions decided that a marshy lagoon at the head of the Adriatic was easier to defend than the towns of the surrounding Veneto mainland. The lagoon was shallow, treacherous to navigate without local knowledge, and inhospitable to large invading armies. The earliest settlements were on the higher islands — Torcello, Burano, Murano. The cluster of small islands that became the historic centre of Venice — Rialto, San Marco, Dorsoduro — was settled progressively across several centuries as the mainland refugees gave up hope of returning home and built permanent towns on what had been a temporary refuge. By the 9th century Venice was a recognisable city. By the 13th century it was one of the most important maritime trading powers in the Mediterranean. The Republic of Venice — La Serenissima — was effectively a sovereign state from the late 7th century until Napoleon ended it in 1797.
The Pilings and the Building Method
The challenge of building stone and brick structures on a lagoon was solved through a remarkably consistent technique. A site was selected and the lagoon mud excavated to expose a layer of stiffer clay below. Wooden pilings — typically 2 to 4 metres long and 20 to 30 centimetres in diameter — were hammered into the clay in tight grids, sometimes packed so close that adjacent pilings touched. On top of the pilings, horizontal timber beams were laid, and on top of the beams a layer of Istrian limestone — a particularly water-resistant stone quarried in what is now Croatia — formed the actual floor of the building. The brick or stone walls above the limestone could then be built with confidence that the foundation would hold. The Salute church and St Mark's Basilica use this technique. So do the Doge's Palace, the Ca' Foscari University buildings, the houses lining the Grand Canal, and essentially every other significant pre-modern Venetian structure.
The technique's success depended on the wood remaining permanently submerged. Pilings exposed to oxygen — for instance, when the lagoon water level drops below their normal height — begin to rot within years. This has happened repeatedly in modern Venice as groundwater extraction in the 20th century lowered water tables and exposed parts of older foundations to air. Several historic buildings have required emergency reinforcement of their pilings since the 1970s.
Acqua Alta and the Floods
Venice has always flooded. The lagoon is connected to the Adriatic through three narrow channels (Lido, Malamocco, and Chioggia), and the tides that drive water in and out of the lagoon are amplified by various combinations of wind, atmospheric pressure, and freshwater inflow from the rivers feeding the lagoon. When all these factors align in the autumn and winter months — particularly during the sirocco wind from the south that pushes Adriatic water northward — the lagoon water rises above its normal level and overflows into the streets and squares of Venice. This is called acqua alta ("high water"), and it has been part of Venetian life since the founding of the city.
Historically, acqua alta events of 80-100 cm above the average sea level were unusual but not catastrophic; Venetian shopkeepers and residents put up temporary wooden walkways and waited for the tide to recede. Events above 110 cm became common by the late 20th century. The catastrophic flood of November 1966 brought the water to 194 cm above the normal level and inundated 96 percent of the city for over 12 hours; thousands of art treasures were damaged, and the disaster forced the Italian state to take the question of Venice's long-term survival seriously for the first time. A 187 cm flood in November 2019 caused over €1 billion in damage and gave new political momentum to the long-delayed MOSE barrier project.
MOSE
The MOSE project (Modulo Sperimentale Elettromeccanico, "Experimental Electromechanical Module") is the engineering response to Venice's flooding problem. It consists of 78 mobile gates installed across the three inlets of the lagoon. Under normal conditions the gates lie on the seabed, filled with water. When a high tide is forecast, the gates are pumped out, become buoyant, and rise above the surface to seal off the lagoon. After the tide passes, the gates are flooded again and sink back to the seabed. The system was first proposed in the 1980s, formally approved in 2003, plagued by enormous cost overruns and a major 2014 corruption scandal that sent dozens of officials to prison, and finally operationalised in October 2020. The first time the gates were raised, they successfully held back a tide that would have caused a 130 cm flood in Venice; the city stayed dry. MOSE has now been raised dozens of times. Its long-term durability is unknown.
The Subsidence Problem
Independent of sea level rise, Venice itself is sinking — though slowly. Natural geological subsidence in the Po Plain accounts for about 0.5 mm per year of downward movement. Twentieth-century groundwater extraction for industrial use on the mainland accelerated this dramatically, causing the city to drop by approximately 12 centimetres between 1900 and 1970 before extraction was banned. Continued natural subsidence and consolidation of the lagoon sediments contribute another 1-2 mm per year today. Combined with about 3-4 mm of annual sea-level rise driven by climate change, the effective rate of relative sea-level rise at Venice is around 5 mm per year — five times the rate the city experienced for most of its first millennium.
The Resident Population
In 1950 the historic centre of Venice (the islands of the lagoon, excluding the mainland districts of Mestre and Marghera) had approximately 175,000 permanent residents. By 2025 the number has fallen below 50,000. The remaining residents face an annual influx of around 25-30 million tourists. The city's economy is overwhelmingly tourism-driven, with traditional industries (glass-making at Murano, lace at Burano, the historic Arsenale shipyards) reduced to nostalgic remnants. Housing has been steadily converted into short-term tourist rentals. Schools have closed for lack of children. Hospitals, supermarkets, and basic services have either consolidated or moved to the mainland. A 2021 decision to charge day-trippers a small entry fee to enter the historic city — implemented in 2024 — was an attempt to manage the tourism pressure, though the amounts have been too small to have significant effects.
The Future
Three roughly distinct futures for Venice are debated among engineers, politicians, and Venetians themselves. The first is the continuation of MOSE and incremental adaptation: keep raising the gates, keep restoring foundations, keep accepting that the historic city becomes a kind of museum-island that loses its residential function but preserves its built fabric. The second is a more ambitious engineering intervention — proposals have included permanently raising the entire city by pumping water under the lagoon floor (technically feasible but extraordinarily expensive), or building an outer ring of barrier islands to fundamentally change the lagoon's hydrology. The third, increasingly discussed but politically unspeakable, is a managed retreat: accept that parts of Venice cannot be saved indefinitely and begin to plan for a future in which the historic city becomes a partially submerged heritage site. No serious actor advocates the third option publicly, but it shadows every discussion of the other two. The city has held against the water for fifteen centuries on the strength of its pilings. The next century will test whether that bet can be extended one more time.