Scientists have spoken: Venice is sinking. It has dropped a foot in the last century. (four inches of that in one swoop, back in the 1950s.) And absent a miracle, it will drop six more feet during this century. 

 What will that look like? Picture St. Mark's Square. Its romantic corridor cafés are doomed to go first. As the lowest-lying point of historic Venice, the piazza could turn into the most grandiose outdoor pool ever created. The mosaic pavement of the basilica? You’ll have to admire it through several inches of water. And the wedding cake–like colonnade of the Doge’s Palace could become a suitable docking point for high-bobbing gondolas.

Venice faces many threats—the limestone stilts on which the city was built are buckling under the long-term stress of all those beautiful heavy buildings, and, ironically, restorations to raise damaged palazzos and sinking alleyways cause the delicate old city to crumble even more—but the most urgent is rising sea levels. So far, the city’s famous seasonal high tide has struck during only some winters, but depending on climate change, it could start to arrive annually and stay for half the year. “That’s the apocalyptic picture,” says Luigi Tosi, a coastal geologist with the Institute of Marine Sciences. Satellites are still gathering data, but the prognosis, he says, is “definitely bad.”

Already, on moonstruck winter nights, water oozes through the tile cracks in buildings' ground floors. When the familiar smell—half fetid, half briny—hits, Venetians know the drill. They sprint into action, moving electronics, wooden tables, and precious curtains to higher ground. If the tide is high enough, business comes to a halt. When it recedes, barmen pull on rubber boots to resume serving cappuccinos.

Venice needs a fix of biblical proportions, which is where MOSE—an acronym that’s also Italian for Moses—comes in. The $6 billion floodgate promises to hold back the Adriatic Sea at each of the Venetian Lagoon’s three inlets. If it sounds crazily ambitious, that’s because it is. Picture an 18-wheeler. Now stack up five of those and paint them yellow. That’s about the size of one MOSE flap. Line up 78 of those, and you’ve got a mile-long modular flood-gate that will rise 10 feet above the lagoon’s water level. “MOSE is like a musical instrument that we’ll be able to play however we want,” says local architect Ettore Vio.

Let's cross our fingers that the instrument is in tune. 

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