A barrier that rises from the lagoon floor
Venice sits inside a shallow lagoon connected to the Adriatic Sea through three inlets. That connection lets seawater flow in and out, but during unusually high tides it also gives rising sea levels a direct route toward the city. MOSE counters those surges by temporarily closing the inlets rather than building a permanent wall around Venice.
At each inlet, rows of large steel panels rest inside concrete housings on the seabed. The panels are hollow. To raise them, operators pump compressed air into the panels, forcing out the water inside. The resulting buoyancy rotates each panel upward on its hinges until it forms part of a barrier across the inlet. To lower the gates, water is let back in, and the panels sink into their housings.
Why the gates are not always up
Leaving the inlets open matters: ordinary tides and currents help maintain the lagoon’s natural exchange with the sea. MOSE is meant to interrupt that exchange temporarily when a high tide threatens flooding, then reopen the passages afterward. That makes the system a movable defense, not a permanent dam.
The tradeoff is that a closed inlet also restricts water movement and vessel traffic while the barriers are raised. The gates therefore protect streets by briefly changing how the lagoon connects to the Adriatic. Their most striking feature is also the key to that compromise: when the danger passes, the steel wall disappears back beneath the water, restoring the open inlets.
