Theories and concepts of horizontal urbanism have come to the fore at different times throughout the history of the city and territory, assembling a dense legacy of interpretations and a very clear tradition of urban phenomena. In this sense, the term Horizontal Metropolis can be read as a connector, as the common denominator of theories and concepts that seeks to unfold an alternative urban condition, going beyond (and not necessarily against) the idea of concentration or accumulation. This chapter collects researches on both theories and historical roots of these urban phenomena.

Researches on different authors (i.e. Geddes, Rosseau, Wright, Branzi, Sieverts, Neuteling), different places (i.e. China, Switzerland, Berlin, Netherlands) and different questions (i.e. globalization, urbanization, sustainability) first of all highlight the effort made in identifying, picturing and describing the Horizontal Metropolis as a multi-scalar process, presenting concepts that are at the same time global and site specific.

Firstly, the global dimension of the Horizontal Metropolis can be unfolded in two different ways. On the one hand, this collection of theories can certainly draw an almost exhaustive world map, in which different terms (such as megalopolis, città diffusa, patchwork metropolis, Zwischenstadt, desakota, hyperville […]) have been used to describe similar phenomena and projects. On the other hand, the Horizontal Metropolis can be conceived in itself on a global scale as a planetary pattern where borders, boundaries and flows blur (Cogato Lanza). And yet this space, despite being global, can be considered to be narrow. If one follows the theories of planetary urbanizationFootnote 1, the Horizontal Metropolis could be considered as part of an up-scaled ‘agglomeration’ landscape, where beyond it, there lies a much more extended horizontality, the ‘operational’ one, equipped for food, mineral, energy and water production and circulation, orchestrated through the operation of logistical networks into global commodity chains. Together, these two horizontal metropolises constitute the vast majority of the ‘used’ part of the planet (Katsikis). This extended idea of urbanization suggests that the same is not only about expanding agglomeration areas or creating new ones, but also about the incrementation of operational areas (such as agricultural lands, resource extraction sites, forests, physical infrastructures and logistic system), which lie today in a condition of geographical interdependence (Katsikis).

Secondly, next to its global (and interlinked) dimension, the Horizontal Metropolis is certainly a site-specific phenomenon: its singular theories and definitions do not seek to outline an ideal or a model of city, but rather to investigate specific characteristics and dynamics of real situations (Pisano)Footnote 2. Indeed, the different definitions for these similar conditions might represent a clue for comprehending the intimate bond within theories and contexts (along with their culture and their urbanisation processes). For these reasons, the Horizontal Metropolis taken as an overall conception should not lead to the idea of the ‘generic city’ nor seek for similarities rather than understanding the intimate relation between history, context and global dynamics (Grojean).

The importance of this interscalar connection is quite clear in the development of the Chinese conjugation of the Horizontal Metropolis, which grew as hybrid, path-dependent and locally constitutive blending of elements from the past with the present as well as the local with the global economy (Lin).

If taken from another perspective, the same concept of site specific can be conjugated with the renewed consciousness for geographical features (versus the idea of ‘tabula rasa’) of the New Regional Pattern of Ludwig Hilbersaimer (Cogato Lanza; Waldheim), or it can find its roots in the social and physical survey of Patrick Geddes (Skyonsberg). Furthermore, the same specificity of sites might also hark back to the global dimension in approaching the idea of ecological region, envisioned by Dokuchaev (1850), Reclus (1895) and the same Geddes (1905) as fundamental for comprehending physical, natural and social facts, and as a whole belonging to a larger system: the world (Durand).

The second main point that this chapter brings to light is that theories of ‘horizontal urbanism’ have come to the fore in different times as intimately connected to processes of transition. Besides the ‘metropolitan bias’Footnote 3 brought by the oxymoron ‘horizontal metropolis’ in itself, the metropolitan condition of this kind of urbanity should be perhaps traced in its attitude towards change (Cogato Lanza), towards economic, social and environmental shifts.

Many processes of horizontal urbanization can be directly related to shifting economies, from agrarian to industrial, or from industrial to post-industrial societies. Curiously, this overview on shifting economies and hence on processes of urbanization does not follow, as might be expected, a chronological order, but rather a geographical one, where once again the global dimension plays a non-neutral role.

On the one hand, one could find theories that, reacting to the process of concentration, foster processes of decentralization of both urbanization and economies.

A first example can be found in Wright’s Broadacre City (1934–35), where, while envisioning a decentralized and democratic society, it represented a model against the process of ‘metropolization’, against the standardization imposed by the monopoly of the metropolis (Maumi). Metropolization for Wright meant the destruction of resources, the ruin of landscape, the disappearance of rural economy killed off by intensive farming, the dying out of local farming. In other words, the metropolis was seen as a form of ‘deterritorialization’ (Maumi), where decentralization, which does not mean dispersion, was proposed as a real alternative to the ‘industrial metropolis’. Like Broadacre City, Ludwig Hilbersaimer’s New Regional Patterns (1945–49) and Andrea Branzi’s Agronica (1993–94) are also conceived on the assumption of an ongoing process of decentralization led by industrial economy (Waldheim). These ideas, visions for a different kind of urbanity (discharged of their utopian, political and social aspirations), went on to partially take shape in different contexts where decentralized economies have led to diffuse urbanization or vice versa, i.e. the città diffusa in the Veneto Region, as defined by Francesco IndovinaFootnote 4; or the Banlieu Radieuse in Flanders, as described by Marcel SmetsFootnote 5; or the Swiss territory where the idea of ‘growing’ dense industrialized cities has been rejected (Tursic).

On the other hand, unlike the situations in the West, where the emerging of diffuse urbanization has been closely intertwined with the transition of the economy and society from industrialism to post-industrialism, the growth of the ‘peri-urbanism’ in the Chinese context of Dongguan occurred alongside the transition from an agrarian society into an export-led industrializing economy, which has lead to a widespread spatial pattern primarily located at the village level (Lin).

Furthermore, the construction of horizontal metropolises refers to a second type of transition, the one related to mobility patterns, to material and immaterial networks (Cairns). The horizontal metropolis is a space of exchange, where a continuous system of relational forces is opposed to a collection of objects (Waldheim), where important flows of people, goods and information go on to become a distinctive characteristic in opposition to those spaces that thrive on accumulation (Grosjean). These multilayered and multi-scalar connections, recalling André Corboz’ metaphor of hypertextFootnote 6, set this kind of landscape apart from that of immanence and multiplication. Hence, it is via this hyper-connected space where diffusion does not mean dispersion, that each fragment encounters its potential meaning (alongside to its nostalgic dimension), becoming part of a whole such as, for example, a patchwork (Pisano) or an archipelago (Veronese). It is indeed this infrastructural support that could build the so-called isotropy Footnote 7, that equal spatial and social distribution of possibilities, that democratic principle (Cogato Lanza) of fair distribution that Wright imagined for Broadacre City (Maumi).

In this sense, the question of democracy leads directly to another type of transition, that of resources, their limit and their alternative. The Horizontal Metropolis, as both any project and de facto urbanized pattern, has come to face questions such as the ‘limits to growth’ or ‘our common future’.

Once again, as an attempt to redistribute goods and to preserve natural resources, Broadacre City represents a pioneer vision, conceived as a ‘transition scheme’, where the use of the resources, the exploitation of the ground and the preservation of nature would be measured for the generation to come (Maumi), anticipating the question of ‘our common future’ and of the sustainability of the planet by more than 50 years. In addition, the 1970s radical environmental thinking clearly suggested the abandonment of cities in favour of an extended, broader, better distributed urbanized pattern (Rebillot). Despite these promising indications, after the UN’s report of 1987Footnote 8, any hope for a synergy between an ecodecentralism and mature (post)industrial urban systems was shelved in favour of a traditionalistic approach committed to the compact city (Rebillot). But the dominance of the horizontal metropolis as both ‘aggregational’ and ‘operational’ landscapes on a planetary scale (Katsikis) legitimates and gives room for exploring the ecological potential of the extended urbanization here described. It is an exploration that could feed both existing and emerging territorial systems (Rebillot), such as the Asian context, revealing the demographic, economic and ecological interdependencies of such regions (Cairns).

The last process of transition that the horizontal urbanism encounters is placed at a theoretical level: it refers to the flows of ideas and references during the construction of its theory and tradition. Over the decades, the exchanges among different conceptions of these urban phenomena have played a fundamental role in portraying, by integration or differentiation, a transcultural tradition,Footnote 9 that perhaps still needs to be investigated in depth.

In short, through contemporary and historical theories, the Horizontal Metropolis emerges as a strong interscalar and site-specific concept, as both a vision and a de facto spatial process that occurred in different contexts in between major shifts in the political, economical and social structures, catalysing clear global and local mutations. The Horizontal Metropolis is the possibility for an alternative and extended urbanism, an open idea of urbanization that brings together a tradition of thought, a resilient rather than unstable (or stable) territorial structure, capable of adapting to both constantly changing conditions and multilayered mutations.