This summer was a summer of firsts for me. I took my first international flight, studied abroad for the first time, and saw my first wonder of the world: the Colosseum. There is nothing quite like stepping out of the crowded Colosseo metro station, located under Rome’s ancient city center, to the astonishing sight of Ancient Rome’s monument to spectacle and extravagance. Lines wind all the way around the amphitheater for entry tickets, and rightfully so. But I would advise you to take a right at the Colosseum’s ticket booth and head toward the underappreciated jewel of Ancient Roman remains: the Roman Forums. For less than 20 euros, you can explore ongoing archaeological digs, enter some of the holiest sites of the Roman Republic, walk upon the site of the first gladiatorial games, and even toss a rose onto the funeral pyre of Julius Caesar.

Above: In the center of the Eternal City, the Roman Forums give tourists and archaeologists alike a window into daily life in Republican Rome. Image courtesy of Katherine Long.

At its peak under the rule of Emperor Trajan, the Roman Empire commanded enormous amounts of wealth, enabling him to wage expensive wars and construct architectural wonders at home, from the Colosseum to the Pantheon. Today, what lies between the Colosseum and the Pantheon is mostly ruin and rubble. Visitors must strain their imaginations to envision the once-great palaces and courthouses from the few measly columns and concrete foundations left standing. Indeed, conservationists have their work cut out for them when it comes to reconstructing and preserving the history of the Eternal City — and they’re even turning to science to discover new tools. 

One of the most notable extant structures in the Roman Forums is the Arch of Septimius Severus. Believe it or not, Septimius Seerus isn’t a character from Harry Potter — he was a Roman emperor who, along with his sons Caracalla and Geta, triumphed over the Parthian Empire in Persia between 194 and 199 CE. He commissioned the construction of the triumphal arch and dedicated it in 203 CE. The arch remains an excellent example of the kind of political propaganda enjoyed by the emperors of Ancient Rome, but it gained another level of historical intrigue upon the death of Septimius Severus. The emperor’s sons Caracalla and Geta had been instructed to jointly rule the empire after their father’s death, but within a year Caracalla ordered Geta’s assassination and took over as sole ruler of the Empire. As part of his rise to power, Caracalla proclaimed a damnatio memoriae of Geta: an official doctrine that ordered Geta’s name and image expunged from all official records and monuments in Rome as an effort to erase his memory from history. This included the Arch of Septimius Severus, making this monument an example of imperial propaganda for two Roman emperors and a relic of the Roman practice of damnatio memoriae.

Above: A view of the Colosseum-facing side of the Arch of Septimius Severus in situ at the Roman Forums. Image courtesy of Katherine Long.

Conservationists thus have a vested interest in preserving this nearly 2000-year-old monument, which has been subject to damage from fire, flooding, chemical fumes, and erosion. In addition, a road built through the arch in the 4th century exposed the arch to damage from traffic collisions. The arch was part of a Christian church for a time, allowing it to be preserved better than other triumphal arches from Imperial Rome. The remarkable skill of Severan Dynasty stonemasons is also credited for enabling the arch to survive to the modern day in decent condition. 

Above: View of the Capitoline Hill side of the Arch of Septimius Severus, with an inscription dedicating the monument, as well as high-relief sculpture and decorative elements across the whole structure. Image courtesy of Katherine Long.

It was only in the 19th century that the arch was fully excavated and restoration efforts began. The arch saw extensive restoration during the first half of the 20th century, followed by maintenance. In the 1990s, archaeologists noticed deterioration of several sections of the monument due to exposure of the stone to atmospheric agents and pollutants, in addition to structural integrity problems caused by earlier efforts at restoration. Micro-cracks threatened the inner stone structure and erosion had pulverized the marble encasing the arch. This necessitated immediate action. Archaeologists sealed cracks by micro-plastering and cleaned pollutant buildup using lasers to avoid exposure of the delicate marble to harsh chemical agents. But one problem remained: without intervention, the stone and marble materials in the arch would continue to crack, and conservationists worried that the structure would eventually disintegrate. Archaeologists wanted to limit the application of foreign materials to the structure, but leaving the monument to fall apart was out of the question. In the last few years, one team has identified a surprising ally in the effort to save the arch: bacteria.

The Arch of Septimius Severus was one of the first monuments treated with an experimental method called bio-consolidation: conservationists consolidated and fortified the stone using carbonatogenic bacteria. Scientists exploited the ability of bacteria found naturally within the stone to produce calcium carbonate, a natural component of marble, to seal cracks and improve the structural integrity of the monument. They treated the monument with enzymes to draw the calcifying bacteria to the surface of the stone. These bacteria moved through the cracks in the monument, secreting a biomineralized matrix of calcium carbonate behind them, thereby restoring the arch at the molecular level. No other application of foreign materials was needed to complete this method of biomineralization restoration.

Above: Detailed view of the Capitoline Hill side of the Arch, with visible degradation of the marble that has been calcified to restore structural integrity to the monument. Image courtesy of Katherine Long.

Bacteria have one more advantage over chemical and physical methods of cleaning and restoring monuments: they do not contaminate the environment surrounding in-situ monuments. Preservation of the environment is of special concern to the conservators working on the Roman Forums, which house dozens of monuments of great legacy and importance. Chemical contamination of the environment could damage or degrade underground structures, weakening the foundation of surrounding monuments and damaging buried structures that are still under investigation by archaeologists. 

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Above: A scientist tests different bacteria strains for their ability to clean marble at the National Roman Museum in Rome. Image courtesy of CNN.

Conservationists recently completed this pilot intervention on one side of the arch and will soon utilize this strategy on the under-arch as well as its other side. The success of this intervention has made waves in the fields of art restoration and conservation, perhaps inspiring its use on other monuments in the future. 

Bacterial restoration strategies have been successfully used on other monuments in Italy. In 2019, conservationists used bacteria to clean several statues by Michaelangelo adorning the graves of members of the Medici family in Florence, Italy. These bacteria were able to remove blemishes caused by oil, glue, and phosphates that had resisted the efforts of conservationists armed with harsh chemical cleaners. A similar method was used to clean in-situ fresco paintings in cathedrals in Milan and Pisa. The success of the teams from Florence, Pisa, and Milan further demonstrates the many ways in which living organisms can help us preserve and conserve our shared cultural heritage.

Above: The tomb of Giuliano di Lorenzo de' Medici, Duke of Nemours is flanked by allegorical sculptures of Night and Day by Renaissance sculptor Michaelangelo. This tomb in the Cappelle Medici was recently cleaned using bacteria. Image courtesy of Aleksandr Zykov.

In several ways, bacteria are helping to conserve the material culture of human history while minimizing environmental impact. Thanks to our microbial allies, generations to come will get to read the millennia-old inscriptions on the Severan Arch and learn the tragic story of Caracalla and his brother, Geta, that shaped the legacy of the Severan dynasty. They will get to enjoy the genius of Michaelangelo’s sculptures, appreciate the legacy of the Medici in Florence, and marvel at the beauty of Renaissance frescoes in historic cathedrals across Italy. Conserving the art our ancestors created is essential for the preservation of our culture and history. Investing in innovative efforts to preserve our shared cultural inheritance is a calculated risk that pays off by counteracting the damnatio memoriae imposed upon each of us by history. The scientists, archaeologists, and microbes that contributed to these restoration projects each had a hand in deciding that every one of the soldiers, stonemasons, senators, and citizens involved in the construction of the Severan Arch mattered. This is one of the most meaningful things that we can do for human beings past, present, and future. A few hundred meters away from the Colosseum, the Arch of Septimius Severus has been transformed into a monument not just to Roman propaganda or damnatio memoriae but also to human innovation: to the power of tiny creatures working together to appreciate and preserve our history for generations to come.