Guarded by glass

Barriers keep Venice’s iconic basilica dry

VENICE, Italy — It’s a simple solution, but one that may keep the marble columns and valuable mosaics of Venice’s iconic 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.

The new barriers are made of glass mounted on a base of armored concrete that is buried below the pavement of the famous St Mark’s square to resist the force of surging water. Piana said the system could keep out up to 3 feet, 6 inches of water in the square, equivalent to a tide of 6.2 feet 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 claybrick structure.

Built on log piles among canals, the palatial city of 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 4.2 feet.

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.

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

Piana said that the glass and concrete barriers were 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.

Signs of erosion are visible Dec. 7 inside St. Mark’s Basilica in Venice.

(AP/Domenico Stinellis) Procurator of St. Mark’s Basilica Mario Piana leans on a glass tide barrier Dec. 7 during an interview with The Associated Press in St. Mark’s Square in Venice, Italy.

Signs of erosion are visible inside St. Mark’s Basilica.

Signs of erosion are visible inside St. Mark’s Basilica.

Tourists and residents walk on catwalks during a sea tide of around 38.18 inches to cross a flooded St. Mark’s Square.

A thin layer of seawater surfaces during a moderately high tide in St. Mark’s Square.

Signs of erosion are visible inside St. Mark’s Basilica.

Tourists and residents walk on catwalks Dec. 10 during a sea tide of around 38.18 inches to cross a flooded St. Mark’s Square in Venice where recently installed glass barriers prevent seawater from flooding the 900-yearold iconic St Mark’s Basilica.

A couple stops on the fragile marble mosaics on the floor of St. Mark’s Basilica, which has for centuries been endangered by seawater, in Venice.