“Architecture springs from dialectic between departure and return. As a wayfarer, man goes by his way, with the task of penetrating the world and working out its inner meanings. This is the sense of the action of settling. (…) Working out [these meanings] here stands for building up the border or threshold, from which a settlement starts its very essence. As the threshold is the junction between outside and inside, and architecture is the incarnation of this junction…”

Defining thresholds: a conceptual instrument for urban design.
The way of defining thresholds and linking spaces is parallel to the process of formation of ideas: each civilization develops an autonomous set of thoughts and a culture which is characterized by the relationship with the inhabited territory and the shape of cities. If we take the urban fabric as the ‘interior’ and the surrounding environment as the ‘exterior’, then it is immediately clear how the notion of their relationship and the one about ‘linking interior and urban environments’ are two design declinations of the same theoretical question: the threshold. Here the writer intends to discuss the first, which deals with urban shape, balance of urban settlement with the territory, urban developments and transformability of urban borders. The relationship with the natural external environment has always been deeply characterizing for the general urban form, together with the permeability with nature in terms of physical structure and linkage between productive urban life and the rural territory. This linkage was governed through the urban threshold, which always has been the transformable medium by which two complementary systems were defined in a continuous balance: city and environment. This we see wonderfully represented in the fresco of Buon Governo by Ambrogio Lorenzetti, in Siena, Tuscany. Threshold as urban edge was in previous centuries the unifying device of the European city and we see that every urban representation until the 18th century was conveyed by the image of its external walls: Isidore from Seville could assert that “Urbs ipsa moenia sunt”, ‘cities are their own walls’. Urban expansions were always limited by a new system of enclosing walls while the previous ones were actively transformed becoming part of the urban fabric. Here we recognize the particular character of the threshold: it is a transformable element, with different degrees of openness and permeability to the exchanges between exterior and interior, yet it always keeps a specific recognizable image, owing to its shape which is not only a shell, but a formal structure. These specific morphologic qualities of the threshold are hard to recognize in contemporary urban transformations, for several reasons: the wider extension of the city, the rapidity of transformations, the insertion of more rigid elements as great infrastructure and productive functions. On the contrary, in history we can find topical examples of intelligent development of the city and redefinition of its thresholds. A particular case is given by the great Renaissance urban additions and those of the 19th century, among which Ferrara and Lucca are of particular interest. In Ferrara at the end of the 15th century, the architect Biagio Rossetti was ordered to design the Addizione Erculea by the governor of the city, Ercole I d’Este: here the urban shape changes radically and reaches a new structure, including and transforming the existing boundaries. As a consequence, the new town trebled the urban area and changed for good the shape of the town from linear, developed along the Po river banks, to a basically pentagonal one. The new urban section is added to the old mediaeval town without clashing or separating, but blending in with proportions within the existing street network. At the same time the new urbanization created new ratios and urban landscapes – the wide and straight roads that are overlooked by churches, mansions and public areas, which are interspersed with gardens an orchards while making the perspective of the street one of great splendour, incorporating within itself landscape fragments.
In the town of Lucca we observe a different phenomenon: the recognizable shape is kept, but the quality of its threshold has changed, from a defensive system into a new public space that circumnavigates the city as a ring park. In the second decade of the 20th century, Lorenzo Nottolini transformed the town walls of Lucca into an aerial promenade and the surrounding free spaces into a treelined green belt which separates the historical centre of the town from the suburbs while preserving its individuality with the modern town. Today we are often asked to find new solutions for transforming the city, solutions which are adequate for each cultural and natural context, for different urban structures and for development issues.
The central importance of the threshold, as an element of discontinuity and linkage, of alteration and coherence, all at the same time, is evident as we recognize that contemporary transformations comprise “dynamic factors prevailing on static configurations, relational scales on dimensional extensions, discontinuity elements on unifying elements..”

Designing Thresholds: Al Ain, transforming a city in the desert. The United Arab Emirates has a unique kind of urban settlement: the city in the desert. While in temperate natural contexts, man has built the city as a concentration of a spread presence of activities in the territory, in deserts urban settlements are completely isolated and have no linkage of control or productivity with their surrounding natural environment. Most times they emerge in the presence of water and oases: which is the case of Al Ain, oases city, where in 2007 the XII edition of the IUSS International Design Seminar “Urban Culture and Landscape Renewal” was held. The opportunity of designing in such a particular place as the desert, led the international student groups involved in the seminar to reflect upon the very essence of the relationship between man and nature, the first essential threshold from which architecture springs.
When can we affirm that we are inside the city and not on its border, if the perception is constantly dominated by the strong presence of the desert? In his novel, The Songlines (1987), Bruce Chatwin hypothesizes that the desert could have been the true cradle in which human intelligence was born. Ancient men moved across the deserts and had to overcome hard, often brutal natural obstacles to their survival – thus they were forced to develop a deep knowledge and understanding of the natural environment in order to create the first places for human settlement. The first act of constructing a village in ancient times concerned the lining or the perimeter walls and the resulting spatial discontinuity created two mutual opposites of interior and exterior. These then developed further into private and public spaces, voids and built volumes. Their dimensions, corresponding proportions and distances all determined the quality and density of the urban fabric, as they are the main characteristics of urban civilizations in different environmental contexts. When the first nomads found the group of oases which embodies Al Ain, they probably felt a sensation of rest never experienced before. The vertical palms rising from the earth invited them to stop, settle down and raise something new skyward. Giedion argues that verticality is the first act of identification of the human field: thus walls and precincts are basic elements for identity of place.
Therefore, the theme of the walls and the precinct, the definition of perimeters and the heterogeneous spaces, act as our key to comprehending the project required for Al Ain oases, which is an exercise involving urban transformation and landscape renewal.
Landscape is an expression which contains multiple meanings, to an extent that reaches out to history itself, as the tracks of men in the space of the natural landscape already make the history of their passage across it tangible. Physical tracks and reference signs in landscape start to set different spaces and when we have difference, we can organize paths and thoughts in time and space, and we can even remember! It is through memory of spatial transformations that place identity develops and carries a deep connection with territory and memory: if thresholds are the topical places of transformation, then they are places for defining and designing the identity of a city.
The design theme embraced the re-use of an area of about two million square metres, running along the border of the major oasis around which the first settlement of Al Ain was born. Today this border is actually very disordered and in some cases apparently neglected by the city – as in the case of the ‘shanty’ village at the southern border near the ‘wadi’ – a no-man’s land which lies in the middle of two different systems, which in turn have no real interaction.
Some public activities lie in this interstitial undefined space: museums, a ‘souk’, and a few strips of residential blocks, while a large urban road encloses the whole plantation area. The resulting image is of disorder and uncertainty, but in reality this space is a hidden structure of the city, a threshold which can be transformed to support urban development. Thus the design theme hides a deeper and important task: how to build a resilient border which can support transformations, yet provide a strong visual and manageable structure for the city.
“The constant activity of rebuilding the city creates a similar problem: the adaptation of the image to the external alterations. As our habitat becomes each time more and more fluid and changeable, it is crucial [for] understanding how to maintain the image continuity through these transformations. How it happens, the adaptation of and image to transformations and what are the limits of its possibility? (…) When does the image break and to what extent? How can this fracture be avoided through physical continuity [of urban space] and how can be fostered the
formation of new images, as the fracture happens? The construction of environmental images, which could be open to variations, is a particular problem: images that are strong yet flexible in regard to the unavoidable strains.”

Transformability and structure of environmental images lie on threshold shapes. Thus the projects developed during the seminar were all based upon a wide reflection of the character of this city in the desert and how it could be expressed in a transformable structure, placed in a unique place, the border of the oases.
At the same time this transformability was intended within the meaning of sustainability; a way of development which guarantees the actual needs without compromising the possible needs of the future (Bruntland Report, 1987)
that is to say, possible future urban transformations.
Different design themes were developed, roughly classifiable through their main defining elements: infrastructure, green ecologic structure, and density.
One project defined a new strong threshold in place of the actual undefined space, by using a macro scale element, an infrastructural wall. This can be considered a form of protection for the green silent oasis from the activities of the city, which is dominated by motor traffic within urban sprawl. The wall therefore fulfils the function of a public way for pedestrians and slows mobility. This large element recalls on one side macrostructures designed by 20th century Italian utopians, and on another the ancient medieval urban walls, then often transformed during the 19th century in many European cities to new aerial promenades, such as in Lucca, and green ring boulevards, as in Vienna. In fact, just as these examples demonstrate, the designed edge-urban wall maintains and illustrates this character of strong structural identity but also of deep transformability.
Two projects defined a softer threshold, by using an ecologic green system which can be eventually extended and become a main structure of development for the whole city. In one case the design proposal uses the rational green grid of a palm plantation to define the development directions and densities of the built urban fabric. The kernel given by the oasis becomes an urban rule of settlement in the desert and recalls the plan for Amsterdam by Van Eesteren, which integrated the heterogeneous town sections with the environment. The town was surrounded by the outer landscape, the Amsterdam forest that became the supporting structure of the town development: in other words, the modern town becomes a park inhabited by built elements. In a second case the threshold was treated differently on the northern and southern borders.
Towards the south there was proposed a new kind of compact urbanization as a contemporary reinterpretation on the concept of an Arabian city, being a great solid mass excavated by light and passages just as the ancient medina, but elevated from the soil, with a ‘pilotis’ structure at the ground level that could leave a free public passage towards the inner oasis. This is a multi-layered threshold with different levels of density and activity, always permeable and integrated with public space, yet providing inner private space for residents. Towards the north the project designed again a green ecologic structure, realizing a soft threshold that could be extended beyond the limit of the actual large road. Residential units are excavated in the soil which is modelled to facilitate the entry of light and air internally, thus creating a new artificial-natural green landscape on the roofs, which acts as a new public space, directly linking the city and the oasis. Thus even here we find another kind of multi-layered threshold, always permeable and structured with public and private levels of urban life, superimposing one on the other.
Three other projects defined the threshold by giving it a new density, with a different grain of voids and built volumes that could be in-filled and transformed in future. One proposal reinforced the boundary of the oasis area, providing an image resembling an enclosing fortress, rather like building a strong threshold, as in the first infrastructural project described above. A second proposal identified a wide operation of urban renewal by extending
the area of the project and restructuring the mobility system, thereby creating a wide, green filter ring around the oasis. New services and residential buildings are here disposed in open and large configurations, thus creating a new urban spatial system, not fixing it, but in fact leaving wide areas that can be occupied later and in-filled. This is a radical proposal for a desert city, as the main approach advocated is one of continuous large extension and a lack of urban densification, because the desert gives no limits to the urban area.
The third project defines a similar strategy, creating unusual patterns of high vertical density that can be filled up without sacrificing the strong image of an urban threshold. Here nine high infrastructural towers designate the edge of the city, facing the natural oasis with the vast desert beyond it: they are not grouped together, yet they are disposed around the northern oasis border, generating a wide spatial void while creating a new urban landscape which is readily recognizable as a space of transition and passage. Moreover this space is not only an internal urban threshold, but a symbolic urban edge, recalling the images given by Steven Holl in his work, Edge of a city, and the words of Giedion concerning verticality, man, architecture and nature: the vertical sign, by its elevation from the ground to the sky, is something of non-natural, which immediately generates a place and a threshold between interior and exterior spaces.


Angelo BUGATTI, Al Ain City, oases city, sustainable city (2007), Libreria Clup, Milano.
Sergio CROTTI, Per un’architettura urbana (1998), a cura, Monti, Bergamo.
Steven HOLL, Edge of a city (1991), Princeton Architectural Press, New York.
Kevin LYNCH, L’immagine della città (2004), Marsilio, Venezia.
Christian NORBERG-SCHULZ, Genius Loci (2007), Electa, Milano.


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