by Alessandra Ressa
Photos and videos by Andrea Tamaro
It’s official: the light at the end of the tunnel for the Theresian Aqueduct has finally been reached. The aqueduct now connects the city center to Trieste’s Karst. Its galleries, located in the San Giovanni district, have been reconnected to the deep recesses of the Karst near the Faccanoni quarry, just as they were over two and a half centuries ago when engineers under Empress Maria Theresa excavated them during the Austro-Hungarian Empire to capture underground water sources and perhaps even reach the coveted Timavo River.
The Theresian Aqueduct is now fully accessible, extending nearly two kilometers, with its most recent discovery revealed just days ago: 200 meters of the Tschebull tunnel, named after one of its designers. For months, speleologists from the Adriatic Speleological Society (SAS) faced numerous challenges in exploring it. However, landslides, floods, debris, and even deep deposits of clay and mud resembling quicksand did not deter the SAS teams. Since last autumn, when access to Tschebull was reopened after more than a century, they have advanced meter by meter, often submerged in water and mud, to reach the final unexplored gallery. Here, where the tunnels move away from the bustling district and descend into the depths and silence of the Karst, speleologists were able to witness the remarkable meeting of flysch, the rock upon which Trieste rests, and the limestone that supports its plateau. This fascinating and rare transition, especially within an artificial cavity, represents an extraordinary geological treasure.
But this latest discovery may not mark the final effort for SAS speleologists. In the terminal section of the limestone, several small cavities were found, which will be subject to future investigations. These could represent passageways to unexplored caves.
This significant discovery, with its implications for future explorations, was announced today in Trieste at the conference “The Hidden Waters of Trieste,” organized by the Adriatic Speleological Society in collaboration with the Municipality of Trieste at the Luttazzi Hall in Magazzino 26, Old Port. The meeting not only reviewed the latest results from underground explorations but also explored various aspects of Trieste’s subterranean world related to water: historical, research, archival, and fauna.
Historian and speleologist Paolo Guglia, author of numerous books on subterranean Trieste, presented an overview of the city’s hypogeal locations connected to water. This was followed by Adelio Paladini, who emphasized the importance of the Municipality of Trieste’s technical archives in research on ancient hydraulic works, with special attention to Trieste’s fountains, particularly those on Via della Zonta and Nuova Dogana. Nicola Bressi, a zoologist from the Civic Museum of Natural History of Trieste, discussed the relationship between the underground and the animals that inhabit it. Marco Restaino, president of the Adriatic Speleological Society, focused specifically on aqueducts, from antiquity to the present, and on the city’s relationship with water. He then introduced the much-anticipated presentation on the Theresian Aqueduct and its recent discoveries, led by Leda Cipriani.
Exploration and Recovery of the Theresian Aqueduct
The recovery of the Theresian Aqueduct began in 2018, driven by the determination of a group of volunteer SAS speleologists. After hundreds of exploratory trips and excavations, by 2022 they had managed to clear large parts of the aqueduct’s long galleries, painstakingly removing over forty cubic meters of water and debris that had nearly blocked them completely. By mid-2023, they had cleared half of the underground structure and secured a section of the gallery that had been blocked by a massive landslide. This new passage finally allowed access to the Tschebull gallery, which is now passable for about 400 meters. Along with the already cleared sections, this resulted in over a kilometer of accessible underground passages. However, another landslide blocked progress after the first 400 meters.
Through a difficult passage, the team managed to continue for several dozen meters into a new, partially flooded section of the gallery. From there, a narrow passage, carefully widened, led to the last unexplored frontier of the Theresian Aqueduct. After nearly a year of hard work, this passage has been made accessible, revealing new, exceptional findings.
“There was evidence of this section thanks to a project discovered in collaboration with the technical archives of the Municipality of Trieste. An old map indicated a continuation of nearly 200 meters beyond the 2023 limit,” explained Riccardo Mincigrucci from the SAS exploration team. A newspaper article from the early 20th century also confirmed the existence of the excavation. Thanks to these clues and the persistence of Adriatic speleologists, particularly Silvio Masè, Riccardo Mincigrucci, Leda Cipriani, and Raffaele Bruschi, the gallery has finally been fully explored after over a century.
The Tschebull tunnel, with its evocative final section where flysch meets limestone, is currently almost completely flooded, but future interventions will lower the water level. “The aim of water seekers until the early 1900s,” Leda Cipriani explained, “was to continue excavating these galleries toward the heart of the Karst to channel the waters of the Timavo or groundwater to the increasingly populous and thirsty city. At that time, however, the underground hydrological situation was unknown, and those last 150 meters excavated into the limestone proved to be a literal ‘hole in the water,’ as no water was found.” Today, we know that the Karst aquifer lies several meters below the Theresian Aqueduct galleries, making it impossible to capture the Timavo’s groundwater.
However, what has been uncovered is probably the only example of a gallery that penetrates flysch, reaches, and traverses limestone—a unique geological laboratory. “What has so far only been hypothesized from surface observations can now be studied directly in this gallery,” said Silvio Masè, SAS speleologist and explorer. “It is like an open book on the geology of our territory, with the pages being the layers we can now read, over 100 meters deep.” Among the layers, interesting fossil specimens have been found and will soon be analyzed. Furthermore, small cavities found in the limestone will be the subject of future investigations. They may indicate passageways to new, unexplored caves.
“This gallery marks the end of a long cycle of work and exploration, but also the beginning of new studies and research!” said Raffaele Bruschi of the SAS exploration team.
“In recent months, we’ve completed several ambitious exploratory projects,” concluded Marco Restaino, president of the Adriatic Speleological Society. “The most recent being this extraordinary success with the Theresian Aqueduct. Despite the significant time and effort we dedicate to exploration, both in natural and artificial cavities, the reward—made up of research and new knowledge—motivates us to continue.”
The event is part of the series “A Light Always On” at the Luttazzi Hall, organized in collaboration with the Municipality of Trieste’s Department of Cultural and Tourism Policies.
