Glass barriers help protect Venice’s famous basilica from high tides

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Glass Barriers Help Protect Venice’s Famous Basilica From High Tides
Installation of barriers has kept the floors of the 900-year-old church dry. Photo: PA Images
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Domenico Stinellis, Associated Press

It’s a simple solution, but one that may keep the marble columns and valuable mosaics of Venice’s famous St Mark’s Basilica safe from seawater-induced erosion: a set of glass barriers installed around the 900-year-old church has kept its floors dry during frequent high tides.

Even after it evaporates, water leaves behind salt crystals that corrode the marble bases of the columns and the floor mosaics, said Mario Piana, the architect and restoration expert in charge of St Mark’s.

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Italy Venice Tide Barriers Photo Gallery
A thin layer of seawater in St Mark’s Square in Venice, where glass barriers protect the basilica from flooding (Domenico Stinellis/AP)

Italy Venice Tide Barriers Photo Gallery
Tourists and residents use walkways to cross a flooded St Mark’s Square (Domenico Stinellis/AP)

The new barriers are made of glass mounted on a base of armoured concrete that is buried below the pavement of St Mark’s Square to resist the force of surging water.

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Mr Piana said the system could keep out up to 3.5ft (1.10m) of water in the square – equivalent to a tide of 6.2ft (1.90m) above sea level.

“Let’s hope that, from now on, there are no more high waters that will touch the base of the basilica,” the expert said during an on-site visit, stressing the fragility of the clay-brick structure.

Italy Venice Tide Barriers Photo Gallery
St Mark’s Square is the lowest-lying area of Venice and is frequently flooded during extreme weather (Domenico Stinellis/AP)

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Italy Venice Tide Barriers Photo Gallery
Architect and restoration expert Mario Piana leans on one of the glass tide barriers in St Mark’s Square (Domenico Stinellis/AP)

Built on log piles among canals, Venice has grappled with flooding since its foundation 1,600 years ago. But, like other coastal areas, rising sea levels and more extreme weather that scientists associate with climate change have meant more frequent high tides.

While the basilica was built on what was one of Venice’s highest points at the time, it now sits on one of the city’s lowest due to subsidence and rising sea levels.

As a result, St Mark’s gets more flooding than most places and remains vulnerable despite the activation of the Moses underwater barriers around the lagoon city in 2020 to protect Venice from floods over 4.3ft (1.3m).

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Italy Venice Tide Barriers Photo Gallery
Signs of erosion inside St. Mark’s Basilica in Venice (Domenico Stinellis/AP)

Italy Venice Tide
St Mark’s Basilica and its bell tower reflect in floodwater in the square (Domenico Stinellis/AP)

Flooding in November 2019 was especially devastating because the water could not recede quickly following repeated deluges, leaving parts of the basilica submerged for up to 24 hours.

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Floodwater getting into the basilica has frequently been happening out of season too, making it all the more vulnerable and pushing officials to devise the new glass barriers as a defence.

Mr Piana said the glass and concrete barriers are part of a larger engineering project to set up a series of channels below the surface of the church and its namesake square to carry off water from the lagoon and keep it from flooding the square.

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