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Bacteria-generated calcite to save millennia-old Roman arch

Rome, Sep 16 (EFE).- A team of specialists restoring the Arch of Septimius Severus, one of jewels of the Roman Forum, are combining traditional methods with a more scientific approach by harnessing bacterial biomineralization.

Some features of the white marble arch dedicated in 203 to Emperor Septimius Severus’ victory over the Parthians, particularly the reliefs, are coming loose, putting them at risk of falling from the structure.

But this use of bacterial biomineralization, which regenerates calcite, a component mineral of marble, is helping the millennia-old triumphal arch to regain some of its strength, the archaeologist in charge of this section of the Roman Forum, Federica Rinaldi, tells Efe.

“It’s an experiment we have put faith in and has fortunately produced the optimal result,” she says of the technique developed by the University of Granada, in Spain.

The generation of new calcite penetrates the marble substrate, binding fragments together in a process that rejuvenates structure.

Geologist José Delgado Rodrigues, an expert in stone conservation, demonstrates this to Efe as he works from the scaffolding erected around the monument to the Roman emperor, the first of North African heritage and father to Caracalla.

“The calcite that had been lost with the degradation of the marble reconstructs with the bacteria that produce an identical mineral. It is a new calcite, but it is the same as what was there before,” he says.

Unlike older conservation practices, the bacterial generation of calcite “works from the inside out, rather than the outside in,” he adds.

The bacterial solution is applied to areas of the structure identified as being particularly fragile. It is left for a week, shaded from the sun to avoid it coming into contact with ultraviolet light but allowing air to pass through, which is necessary to keep the microorganisms alive.

Restoration work on the north face of the arch is almost coming to an end three months after it started. The team of specialists will then turn their attention to the other facade.

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