The opening of the Principia Archaeological Park in Rijeka, in February 2014, enriched the topography of ancient sites on the Adriatic’s eastern shore, adding a monumental locus, unique in the type and the shaping level of presentation. As for the type, the Principia was an architectural and town-planning element of castrum, a Roman military encampment or town, one of the many scattered along the boundaries of the Roman Empire (limites). In Dalmatia, only fragments of no more than two castra, those of Burnum and Tilurium, have been preserved, not the entire complex as is the case with Tarsatica. As for the shaping level of presentation, the intervention is a result of a public competition and a creative authorial concept, which was meticulously elaborated, and implemented in a controlled fashion.
The Principia, the military headquarters, was the administrative and the religious center of the castrum and its only public space. It is accentuated by being located in the very spatial center, at the intersection of major communication routes: the wider, the via principalis (or the cardus maximus), and the narrower, the via praetoria. Typologically, it derived from the civil architecture of the forum, and represents a version of a town square, which was simplified and adjusted to its function. Its central part was an uncovered, rectangular inner courtyard (the square, or carré) surounded with porticos, behind which spread the facilities with a utilitarian function. Dominating on the front side was the representative building of the military headquarters (the command staff), while the main gate, the Porta Principii was located on its central axis. The main building housed the administrative premises: the offices of city officials (the Tabularia), the officer quarters (the Scholae), the shrine of the flags, and the raised platform (the Tribunal), from which the military commander spoke to the troops. The square was also the venue of major meetings, counseling, and trials.
Building of the Principia at Tarsatica dates from the reign of the Emperor Gallienus (253–268), when Tarsatica gained importance as a strategic point in the defense of Italy. In the next, 4th century, Tarsatica was most likely included in the border defense system of the Empire known as the Claustra Alpium Iuliarum, the Barrier of the Julian Alps. In the late 4th, or early 5th century, the Principia was destroyed and abandoned, and was not repurposed for another e.g. civilian usage. The town itself managed to recover in late 5th century, and survived until the year 800, when it was destroyed in the name of vengeance for the death of Eric, the Duke of Friuli. It was not until the 13th century that Rijeka Svetog Vida was founded on the site of the ravaged Tarsatica. In the following centuries, a new urban structure of a different, and significantly smaller, scale would grow on the ruins of the Principia. Smaller residential houses were built within the preserved perimeter walls and in the once open part of the town, while the ancient layer was destroyed by digging canals and refuse pits.
A well-preserved relic of the Principia, the Roman arch in the Stara vrata Street – built from partially dressed stone, entirely without mortar, 4.5 m in height, and 2.75 m in diameter – has always attracted researchers. For some time, it was thought to be a triumphal arch, then a town gate. After World War ii, when the Old Town was badly damaged by bombing, the remains of ancient architecture emerged from the ruins. In 1955, after demolition of the buildings next to the Church of St. Fabian and St. Sebastian, emerged the walls of the western perimeter of the Principia. The explorations conducted in 1979 confirmed that the Roman arch belonged to the main gate to the Principia. The archaeological and conservation work carried out at Trg pod kaštelom Square, in 1995, unveiled the exquisitely preserved, five-meter-high walls, while the 2004 preservative archaeological research at the Julije Klović Square, along the axis of the gate to the Principia, unveiled the remains of the ancient pavement. New explorations, entrusted to the Croatian Conservation Institute in 2007, encompassed the entire area not covered by existing buildings or communications: a total of 488 sqm, roughly a quarter of the entire complex area. The excavations included a stone-paved courtyard, a portion of the side courtyard with a staircase, four side rooms with stone sills, and a monumental stone front of the headquarters building with stairs. The findings fit entirely into the present fragments: the monumental main gate with the large stone arch, the western and northern perimeter wall of the complex. The data obtained in this, as well as in the previous studies, enabled an approximate restoration of the plan and the possible visual appearance of the Principia. The research results were presented to the public in 2009, in an exhibition entitled Principia at Tarsatica / Late Roman Headquarters, and in an eponymous scientific monograph, which included the contributions of sixteen scientists, and an extensive pictorial documentation.
A year earlier, in 2008, a public competition was held for the architectural presentation and organization of the Principia. Nenad Fabijanić was awarded the first prize for his conceptual design, and was entrusted with detailed design on the basis of his winning proposal. The implementation of the project started in 2013, and, as previously mentioned, was completed in the early 2014. The total cost of the project, from the archaeological excavations to the completion of the archeological park, accounted to more than hrk 15 million, while the resources allocated by the Croatian Ministry of Culture amounted to hrk 150,000. The City of Rijeka has systematically invested in the Old Town. So far, restoration work has been completed on a number of squares and streets, which has involved the presentation of earlier layers, wherever they are available, and has generally extended to the restoration and the preservation of architectural monuments as well. This program of the City of Rijeka is an effort to present an important part of its older urban heritage, while at the same time making efforts to rehabilitate its equally extensive industrial heritage. The Principia is among such major and more important projects which add a new point of identity to Rijeka’s historic urban core.
In his professional past, architect Nenad Fabijanić was repeatedly confronted with the historic environments of the Croatian Adriatic cities, whether it be ancient, medieval or Renaissance heritage, archaeological sites or public spaces, or squares and waterfront promenades. His completed projects testify not only to his refined creativity, his knowledge and respect for the heritage, but also his uncompromisingly contemporary expression. In other words, he creatively intervenes in the historic environment and its monumental values, and is not afraid of contrasts, and of testing the limits. In Rijeka’s Old Town, he was faced with a specific situation: because of serious damage the original historic urban substance suffered during World War ii and of the infill buildings erected within the process of reconstruction after the War, the Old Town acquired a hybrid character. This combination of the historical and the contemporary in the historic core is particularly ungainly in the area of the Principia, where the multi-story Jadroagent office building located at Julije Klović Square, and built in the period 1977–1983, penetrates like a wedge into the tight space of the Principia. Its basement, moreover, hides a Roman barn – sealed with concrete. At the same time, the Old Gate, the main entrance to the Principia, remains structurally compromised by the same building on its eastern side, and the presentation of the Old Gate is impossible because of its presence. The morphology and size of this structure epitomizes the approach to reconstruction taken in the 1960s and the 1970s, and the understanding of contextuality of that time, on behalf of which mushroomed the new, in some places devouring the delicate old fabric. Yet, the Jadroagent building is a fact that one has to reckon with, no matter how spontaneously the idea comes to one’s mind that demolishing it would be a good thing, which actually happens in some European historic environments.
To the northeastern side, and on the very edge of the area, the ancient pavement is occupied by a relatively small and substandard residential house preventing its presentation. This house is a remnant of a block of houses in Pod voltun Street, which were demolished due to their state of dilapidation. The house was upgraded and completely rebuilt in 1929. Oriented towards the archaeological site with its blind gable wall, this abandoned, decrepit and dilapidated property is devoid of any stylistic and morphological characteristics. In short: it has no architectural value. According to the rules of the competition program, it was left to the discretion of the designers to decide whether they wanted to remove it, for which they all opted. In its place, Fabijanić proposed a lightweight metal canopy, a pavilion, or a tent, in which to display a scale model of the Principia. Later, as the design process progressed, the design passed the verification of the Croatian Council for Cultural Goods, but the Conservation Department in Rijeka opposed the demolition of the questionable house, their reasoning being that the house was a cultural object; there were references of interventions from previous periods discernible in the structure of the wall and the fragments, among them, the refuse pit, carved into the host rock, and the portion of the staircase in the basement of the structure. According to Fabijanić, Hardly sufficient to qualify as cultural goods. He engaged in a long-lasting debate with the conservationists. He based his reasoning on a decisive stance: Our goal is the restoration of the oldest urban layer, and the Roman architectural structures. Whatever is found on the site, cannot be more important and more valuable than antiquity. Fabijanić was left without reply to his direct question about the rationale for the inclusion of the questionable house in the cultural heritage, or to his claim that the documented features of the traces of the past were confused with cultural and artistic value, yet, received detailed instructions on the restoration of the questionable house. He did not receive a reply to his reaction to such dictate either, having asserted that the house in the former block would thus become a solitary structure on the edge of the Principia, hence a new development and a hybrid.
In defense of his vision of the Principia, Fabijanić touched the hot topic of the relation between the conservationists and the architects, which heats up with virtually any intervention in the monumental environment. However, the procedures required by the conservationists often demonstrate a certain attitude, rather than the understanding of the singularity of the locale, the ambiences, or the object on which to intervene. The rigidity of the conservationists is often based on outdated stereotypes, and observed in all cultural milieus, from Zagreb to Dubrovnik, from Istria to Slavonia. Such rigidity does not produce the best results, and certainly hampers a kind of creativity we admire in the restoration of historic European cities. Instead of a dialogue between heritage preservationists and innovation bearers, which architects indeed are by the nature of their work, there is only and exclusively the authoritarian, general, a priori attitude with restriction being the dominant approach.
The issue of the house in question has not been resolved. At the request of the conservationists, it was statically protected during the construction. Instead of rather questionable quasi reconstruction, Fabijanić even offered, in the name of compromise, to design a new structure, which would outline the size and shape of the existing small building, of which the back wall would remain preserved as a backdrop. Its function would be similar to the originally proposed porch roof. For the time being, the fate of the scaffolding-surrounded house remains unresolved. Also unsolved remains the issue whether it is possible to open the courtyard of the residential house to the east of the Old Gate, where there are remains of the Principia, which would thus complete the presentation.
But regardless of these unresolved issues, the archaeological park, or the Principia public square belongs among Fabijanić’s best creative designs, which demonstrate his most careful study of the historic environment, of the formal, symbolic, and urban characteristics of its individual parts. His design of the Principia is also marked by a fine balance between the old and the new, the functional and the symbolic, which is generally inherent to his approach. The new is, as a rule, expressed with restraint, almost asceticism, with the aim of highlighting and evaluating the content to be protected, which is actually the meaning of the intervention, and the mission behind the rehabilitation of the inherited in general. Like many of his colleagues in Europe and worldwide, Fabijanić believes and shows that it is precisely in the dialogue with historical and pre-existing values that the specific, individual quality can occur. The Principia is a novelty that has already proven itself as a value and a locus in the urban image of Rijeka.
The concept is based primarily on the idea of highlighting the archaeological area by strengthening its margins, by some kind of framing in order to present it, in the middle of the existing fabric, as a homogeneous whole, or – new individuality. It is, furthermore, based on the striving towards the opening and the shaping of the access way, which means establishing the original straight entrance from the east through the monumental Old Gate, and another entrance, along the western rim to the Church of St. Fabian and St. Sebastian, which must climb the ascent, embodied by two main levels of the Principia. Also related to this is the designation of the points, which offer the most interesting views, that is to say, experience of the site, primarily from high positions, along the said Church of St. Fabian and St. Sebastian, and from Pod voltun Street. This is where Fabijanić confirms the already proven principle: distinguishing between historical layers and constructed elements, their materials, and their processing. In the archaeological zone, which is paved with massive, larger format stone slabs, he refrains from using stone, from repeating the grid. Access ways and stairs are lined with bright, fine-grained exposed aggregate concrete, other pedestrian communications with smaller stone blocks in a different type of grid and module, depending on the slope of pedestrian surfaces. Instead of the usual granite in most other pedestrian areas, this area is dominated by Kirmenjak, the bright Istrian stone, once popular in Veneto – in two or three shades. In short: the selection and use of materials are determined by the site, the structure and texture by the purpose. All the materials, stone, brick, terrazzo, mosaic, plaster, and all the colors are brought into dialogue while the original fragments are allowed to be the loudest. In principle, as elsewhere, Fabijanić always separates the new from the old, highlighting the contrasts between materials and their processing, mainly solid and robust, of old structures, and between the thin, the thinned new, mainly metal and glass, which ensure clarity and elegance.
The archaeological park can best be seen from above: from Pod voltun Street, with a small fence extending into a small esplanade, offering a view of the restituted surface of the square, of the conserved structures and shapes, of all that remained of the Principia. A different experience is provided by a gradual ascent through a wide ramp, a staircase, so to speak, that leads to a belvedere terrace, cantilevered drawn in the extension of the once blind alley along the Church of St. Fabian and St. Sebastian, on the very perimeter of the site. This ascent is separated from the neighborhood by a fence of slender, densely packed, high white joists, which allows a view of the texture of the perimeter wall of the Principia. Along this entrance, Fabijanić found a place for the green area, where three cypresses are planted. The murky green verticals discreetly symbolize the memorial; they are the native plants of this climate that border the roads, mark the cemeteries, point to the long duration, the proof of which is the Principia itself. The entire ambiance is gleaming white: white is the stone, white is the cement, white is the exposed aggregate concrete, white are the floor surfaces and fences. At night, when the illuminations are turned on, a wide variety of effects are possible. They will be shown in theatrical events and various spectacles that are expected to take place at the Principia. The audiences will be able to watch them from all sides, and from the central plane itself. But the scope of possibilities is yet to be tested. In any event, the Principia provides challenges as a new, offered, public, and cultural scene.
 Burnum, a Legion camp, located in the village of Ivoševci near Knin, and Tilurium, located in the area of the village of Gardun near Trilj, date back to the 1st century. The archeological excavations of Burnum began in 1912 and 1913; the work was resumed in 1973. Since 2002, the site has been systematically researched; two arches of the principia portico have been preserved. Tilurium has been systematically researched since 1997. The remains of the camp, located in the area of the site, have been conserved.
 Demolition (German: Rückbau) is the tearing-down of buildings in the era of the forced restoration of destroyed German historic towns with the aim of repairing and achieving contextuality by means of more thoughtful construction practices.