Fortification Sv. Katarina A

A hill above the Rječina River canyon, Rijeka, Primorje-Gorski Kotar County, Croatia
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Year of build:
Original name:
Angheben I
Military architecture
Past and Present Ownership of the Building/Site:

Public (RH, Ministry of defence and City of Rijeka)

Typology and Style

A World War II military fortification facility, built as an underground stronghold consisting of a system of subterranean tunnels and combat blocks (bunkers) on the surface. One of the few completely finished buildings in the area of the city of Rijeka was built between 1931 and 1941 ("Circular 200") and constitutes an integral part of the steel and concrete defence belt, also known as the Vallo Alpino (translated Alpine wall), built by the Kingdom of Italy at its borders during the fascism period. The purpose of these fortifications was to protect their own borders.

“…The stronghold “Sv. Katarina A" consisted of two fortifications known as “Centre no. 1” and “Centre no. 2”, built inside the hills above the Rječina River canyon, overlooking the port of the town of Sušak, and connected by an underground passage of some 160 metres in length. The strongholds were fully autonomous and ready for prolonged resistance, even in the event of being completely surrounded by the enemy.”

Given the typology of the building, fortifications of this type were built in the highest secrecy and were inaccessible to the local population. Apart from being physically inaccessible, the massive surface structures were skillfully camouflaged and thus almost impossible to locate.

“…Other heavy machine guns were housed in steel domes (casemates) with a single embrasure, built into the hillside slopes and carefully camouflaged. Two steel observation domes were camouflaged in limestone and could also serve as positions for light machine guns.”

From: TONIĆ V., Tragom „Alpskog bedema“ u Rijeci i Hrvatskoj, Rijeka: Slobodna Država Rijeka, 2011

Degree of preservation and status of protection

Fairly well preserved. Unlike other fortifications of this type, the final branches of the Katarina A tunnel were obviously built with a smaller ground layer as the tunnel vault at the points where the exits towards the observatory or embrasure are located is made of steel elements. These have corroded due to moisture and their degradation is evident.

One of the halls that once provided shelter for the crew is in extremely poor condition due to the leakage of leachate into the ground, and cracks of a few centimetres can be seen in the vault, and some (so far smaller) pieces have separated. Due to the humidity and drainage of water into the room, the floor has also been destroyed.

What has been found to be in good condition are the steel domes of the observatory and the casemates, where the engraved inscriptions "FIAT" with the year of construction, as well as the inscription "Fonderia Milanese di Acciaio" can be seen.

This has no status as cultural heritage. The characteristic of the extremely long corridors in these tunnels is that they are "carved" by the niches in which the benches are set up. Most of the benches have been destroyed by vandals. Rubbish has accumulated in places of above-ground openings (exits, entrances, bunkers with larger openings), indicating human presence despite it being a controlled area. The partition walls within the crew quarters have been removed, except for that of the tank.

Architectural Description

This building was completed and consists of an underground part made up of a system of corridors connecting combat blocks (bunkers), where their surface part (concrete or steel) was masterfully camouflaged. The length of the main central tunnel connecting the end points of "Centre 1" and "Centre 2" is about 160 metres, while the total length of underground tunnels with all the secondary branches is about 1000 metres.

Considering the size, content and number of premises, it can be assumed that both "Katarina A" and "Katarina B" were the main fortification centre in the area. Namely, with a complete system of bunkers, “Katarina A” also had the crew quarters necessary for longer stay in the underground fortifications in case of a siege situation.

These include the officers' and NCO’s quarters, a kitchen, a water tank, toilets, an electricity generator, a kitchen and a photophone that allowed visual communication with surrounding fortifications. Ventilation in the tunnels had been provided and there were air filter sin every quarter. There was also a steel safety gas-proof door at the entrance. The width of the crew quarters was 3m and the length varied depending on location (10, 15, 20, 25 metres).

“Armament of fortification no. 1 consisted of both heavy and light machine guns located within 6 combat blocks (bunkers): two concrete blocks, each with three embrasures, one steel dome with one embrasure, two heavy machine gun blocks protected by a 20 cm thick steel shield and a steel observation dome also capable of serving as a position for a light machine gun. The first two blocks were intended for the observation/defence of the west side and were built as massive surface structures. The remaining bunkers were oriented towards the much more dangerous east, so the Italian art of camouflage came to the fore with the use of limestone blocks to create the illusion of a coastal dry stone wall, or by digging the position to such an extent that the embrasure could only be seen from the immediate vicinity. In addition to the steel observation dome, this fortification also had a separate reinforced concrete observatory, which was used to indicate firing from both fortifications ("Osservatorio comandante"), which was built almost at ground level.
Armament of fortification no. 2, located on Sv. Katarina, consisted of both heavy and light machine guns housed within 6 combat blocks (bunkers), and an underground artillery battery of two 75 mm calibre guns in steel casemates, 27 calibre barrel lengths (2025 mm) were made according to the Krupp's license. These steel casemates, made at the Vanzetti foundry in Milan, were the most heavily armoured parts to be installed in the “Alpine wall” fortifications.“

From TONIĆ V., Tragom „Alpskog bedema“ u Rijeci i Hrvatskoj, Rijeka: Slobodna Država Rijeka, 2011

History and Historical Context

As consolidated by the Treaty of Rapallo in 1920., a border was passing through the City of Rijeka dividing the city in two parts. The western part that included Rijeka with its harbour was under the Kingdom of Italy, while the eastern part including Sušak and the river Rječina was assigned to the Kingdom of Serbs Croats and Slovenes (treaty of Rome 1924.).

The part of the frontier that was passing over the hills above Rječina river was heavily fortified by some of the main defensive corps of the so-called line “Vallo Alpino” (Alpine Wall).

“In the climate of mistrust that prevailed among European countries in the 1930s, memories of the First World War slaughters were still fresh. The battles on the Italian-Austro-Hungarian front, on the Soča River and in the Julian Alps, could be compared with the fierceness and magnitude of the tragedy of hundreds of thousands of lives lost to those in the plains of France and Belgium. After the war, there was an opinion among military strategists that it was better to invest in strong defensive lines and concrete fortifications than to count on the masses of soldiers, "cannon fodder", as a guarantee of inviolability of borders and avoiding future bloodshed.
The construction of permanent fortifications on Italy's "Eastern Frontier" began shortly after Circular no. 200 was issued: both Croatian and Slovenian papers of that time mention the digging of "huge caverns" as early as in 1931-1932.
“On April 28, 1937 (valid retroactively since December 20, 1934), a decree was issued to found a special corps of the Italian army called "Guardia alla Frontiera" (Border Guard), in order to occupy the positions situated on a line known as “Vallo Alpino” (Alpine wall). This corps was territorially divided into so-called. sectors, totalling 27, from which the first was located on the border with France on the Cote d'Azur, to the twenty-seventh, which was the city of Rijeka itself.”

From TONIĆ V., Tragom „Alpskog bedema“ u Rijeci i Hrvatskoj, Rijeka: Slobodna Država Rijeka, 2011

The fortification was under control of military forces until 1995. However, the only period when it was used for military purpose, was in the “Battle for Rijeka”, from the mid April to beginning of May 1945. (03.05.1945. Liberation of the city of Rijeka from German occupation).

Values of the Building

This site has a primarily historical value, both globally and locally. However, its architectural value is not to be underestimated either. If we take the years when it was built into account, the complete secrecy that accompanied its construction, and the extremely demanding location on the slopes of the Rječina River canyon, we can safely say that from a construction point of view, this facility is an exceptional example of 20th century fortification construction. It is fascinating that the above ground steel domes are about 20-30 cm thick, weighing tens of tons each, it certainly makes it difficult to mount them in secret, especially since they are located on the most prominent and inaccessible slopes above the city.

Description of the Urban Context and Development

There is a fortification with all its parts on the slopes of Sv. Katarina hill, above Rijeka. The entrance is very well hidden and completely overgrown. Although located on the edge of the construction zone of the residential area, almost all parts of the complex are within the area controlled by the Ministry of Internal Affairs, and access to the facility is restricted and impossible without the permission of the guards.

New Cultural Tourist Offer Focused on Selected Building/Site

Since the facility has limited access due to its being located in a controlled and fenced off area that is under the jurisdiction of the Rijeka Police Directorate, the facility as such cannot be included in the tourism program. Although it is one of the more attractive and rarely completed fortifications, it would be advisable to consult with the Ministry of Internal Affairs in order to present it.


The archival documentation for the construction of tunnels and bunkers was not found in the State Archives, which is logical given the fact that the construction of these facilities was a very well-kept secret at the time. It is not possible to exclude the possibility of archival documentation on the Rijeka fortifications in the military archive in Rome, however, a longer period for research is needed. The found documentation comes from private sources or Drenova Heritage Museum digital archive.

Katarina A Approximate Floor Plan