Glass barriers keep St Mark’s Basilica dry during Venice floods | Venice

It is a simple solution, but one that may keep the marble columns and valuable mosaics of St Mark’s Basilica in Venice 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 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. Piana said the system could keep out up to 1.10 metres (3ft 6in) of water in the square, equivalent to a tide of 1.90 metres above sea level.

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

The palatial city of Venice, built on log piles among canals, 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 the climate crisis, 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 because of subsidence and rising sea levels.

As a result, St Mark’s is flooded more than most places and remains vulnerable, despite the activation of the Mose underwater barriers around the lagoon city in 2020 to protect Venice from floods over 1.3 metres.

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.

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

Piana said 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.