Venice, Italy, is situated upon 118 small islands that are separated by canals and linked by bridges. With tide waters expected to rise to perilous levels in the coming decades, the city has constructed 78 giant steel gates across the three inlets through which water from the Adriatic could surge into Venice’s lagoon. The panels — which weigh 300 tons and are 92ft wide and 65ft high — are fixed to massive concrete bases dug into the seabed.

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