The iconic Porta Nigra in Trier has been undergoing renovation since the beginning of the year. The restoration is expected to last around two years and cost approximately €1 million.
This is not the first time the nearly 2,000-year-old structure has undergone renovation, but this time the work is intended to be particularly thorough. Project manager Brigitta Coen explained that the timing is due to current damage affecting both the mortar and the stone, which is now being addressed.
Coen added that these deposits behave differently from the original stone, which could lead to further deterioration in the future if left untreated. The black crusts covering parts of the monument are being carefully broken down using laser technology.
Coen also noted that, over the years, some restoration methods used on the Porta Nigra would no longer be considered appropriate today. She explained that previous approaches attempted to remove all surface layers down to the original stone, which risked damaging material that had built up over centuries.
According to Ulrich Bauer-Bornemann, who is working on the site with laser technology, problems arise when these black crusts become so dense that the stone can no longer naturally absorb and release moisture. He explained that this creates pressure within the material, which is exacerbated by frost and can ultimately cause the stone to crack. To prevent this, laser techniques are used to target only the more recent deposits, leaving the historic layers intact, he said.
The work is time-consuming and requires patience. The total surface area being treated amounts to around 2,000 square metres, and cleaning just one square metre can take between one and two hours, according to Bauer-Bornemann. In total, this represents an estimated 2,000 to 2,500 hours of work.
However, renovation does not mean restoring the monument to a lighter colour. Coen emphasised that the Porta Nigra will remain black. The aim is instead to address the damage and its causes, in the hope of preserving the structure for decades to come.
