The Tunnels of Claudius

The Tunnels of Claudius ( Cunicoli di Claudio ) is a hydraulic work consisting of a long underground tunnel, six sloping service tunnels and 32 wells. It was built on the orders of Roman Emperor Claudius in 41-54 D.

the tunnels

The work is found in Abruzzo, a region in southern Italy, and is considered one antiquity’s grandest hydraulic enterprises. Until the Fréjus Rail Tunnel was finnished in 1871, the Tunnels of Claudius’ underground tunnel was the longest tunnel ever built. (The Fréjus Rail Tunnel is a 13.7 km long tunnel through Mont Cenis in the Alps, which forms an important link in the railway connection between Paris and Rome.)


The Tunnels of Claudius were built to control the levels of Lake Fucine in Abruzzo, to protect human settlements along the lake from flooding. The tunnels also made it possible to divert water and make former wetland areas suitble for agriculture.

Once the Tunnels of Claudius had been taken into use, lake water flowed out through Mount Salviano from the Avezzano side through the nearly 6 km long underground tunnel, eventually reaching the River Liri on the other side of the mountain, by the town Capistrello.


As early as the reign of Julius Caesar, the local Abruzzo inhabitants, known as Marsi, petition the imperial authorities and demanded that they did something to prevent the flooding of the lake. The only natural swallow-hole, located at Petogna, was frequently clogged. Receding lake waters often made large areas of land marshy and caused sanitary problems for the inhabitants.

A plan was drawn up for a project that wouldn’t just deal with the floodings, but also create a road that would connect the Tiber river with the Adriatic Sea, via the Apennine Mountains. Julius Caesar’s assasination, however, put a spanner in the works and the plan was never put into action.

Eventually, another plan was created, one that would involve digging a canal that would make it possible for water from the lake to flow out through the low Cesolino hill and empty into the River Salto. This plan was scrapped since such a diversion of the lake’s water it would increase the risk of flooding in the city of Rome (via the rivers Velino, Nera and ultimately Tiber).

A third plan was deviced, one that would be much more difficult to carry out but that would not pose a treath to Rome. With this plan, water from the lake would be led inside a tunnel through Mount Salviano to the River Liri.

tunnels of cladius

Emperor Claudius

In 41 AD, Emperor Claudius secured public financing for the ambitious Mount Salviano tunnel plan and selected a Roman enterprise to carry out the job.

The project took eleven years to complete and involved around 30,000 digging men, of which some were slaves.

The collateral tunnels were excavated first, and connected to each other by inclined shafts. After that, the main tunnel could be constructed.

The project ran into many problems along the way, including several landslides.

When the project was finally completed, Emperor Claudius claudius held a public celebration that included a staged naval battle on the lake. Both his wife Agrippina and his young relative Nero (who would one day become Emperor Nero) were present when the locks were opened, by Claudius, for the very first time.

The Tunnels of Claudius caused the lake basin to shrink by some 6,000 acres. The risk of flooding dropped dramatically and new land was made available for agriculture. We can see that the economy of settlements such as Marruvium, Alba Fucens and Lucus Angitiae improved significantly.


As the Roman Empire lost control of the area during the Age of Migration and Barbarian Invasions, maintainance of the Tunnel of Claudius stopped, which resulted in it being clogged. The earthquake that occured in 508 AD probably also damaged the work.

As a result of the hydraulic work not functioning anymore, the water levels of the Fucine Lake returned to how they used to be before the drainage was put in.


Several failed attempts were made to restore the water drainage; including one by Frederick II of Hohenstaufen in the 1200s and another one by Ferdinand I of the Two Sicilies in 1790. Both projects were plagued by a lack of funds and an insufficient understanding of the complexity of the undertaking.

In the 1820s, the Italian engineer and architect Cavaliere Luigi Giura and Commendatore Carlo Afan de Rivera tried to at least partially fix the emissary, supported by King Francis I, but it wasn’t until Prince Alessandro Torlonia of Civitella-Cesi (1800-1886) got involved in the 1850s that something substantial actually happened.

Prince Alessandro Torlonia of Civitella-Cesi (1800-1886) order the construction of a new hydraulic work, starting from the monumental inlet Incile del Fucino near the lake south of Avezzano. This project, which was successful and resulted in a more than 6 km long working drainage canal, largely followed Claudius’ immisary and emissary and was concluded in 1870. An major reason for the success of the project were the Swiss engineers Franz Mayor de Montricher and Enrico Samuele Bermont, and the French deputy site engineer Alessandro Brisse. A gradual drainage of Lake Fucine commenced in 1873, with reclamation of land ending in 1875-1876 when the 16,000 hectares of Lake Abruzzese, Italy’s third-largest lake, had been completely drained. The lake was officially declared drained on 1 October, 1878.

The Fucine plain proved highly suitable for growing cereals, vegetables and sugar beets, and many of the lake’s former fishermen turned into farmers.

National monument

The hydraulic work was declared an Italian national monument in 1902, and the tunnel area is considered a site of archeological and speological interest. In 1977, the Archaeological Park of Claudius was inaugurated here in order to protect the site. The park lays between the entrances to the tunnels and the Fucine Inlet.


  • The total length of the underground emissary is over 6 km, with a drop of 8.44 metres and an average gradient of 1.50 m/km in the stretch between the entrance to the Fucine Inlet and the exit of the Capistrello.
  • The average flow rate is 9.09 cubic metres per second.
  • A large statue of the Immaculate Conception of the Blessed Virgin Mary is situated above the three-vaulted bridge of the sluice gates at the emissary head of Borgo Incile.