We could define ‘city’ as a concentration of population, activities, buildings, and infrastructure. Such a concentration can produce different forms of spatial organisation depending on the cultural context; often, a city can evolve quickly and witness dramatic changes in size and layout. In fact, most cities at a certain point of their existence undergo phases of rapid expansion which can blur the distinction between ‘city’ and ‘countryside’, producing complex in-between territories.

The word urban is increasingly used to define this blurred space. Françoise Choay defined our contemporary condition as ‘the civilisation that casts itself on a planetary scale, erasing the ancestral difference between rural and urban’.

And so, in Le città invisibili (1972),3 Calvino offers a thought-provoking portrait of the almost-invisible urban by describing Penthesilea:

To tell you about Penthesilea I should begin by describing the entrance to the city. You, no doubt, imagine seeing a girdle of walls rising from the dusty plain as you slowly approach the gate, guarded by customs men who are already casting oblique glances at your bundles. Until you have reached it you are outside it; you pass beneath an archway and you find yourself within the city; its compact thickness surrounds you; carved in its stone there is a pattern that will be revealed to you if you follow its jagged outline.
If this is what you believe, you are wrong: Penthesilea is different. You advance for hours and it is not clear to you whether you are already in the city's midst or still outside it. Like a lake with low shores lost in swamps, so Penthesilea spreads for miles around, a soupy city diluted in the plain; pale buildings back to back in mangy fields, among plank fences and corrugated-iron sheds. Every now and then at the edges of the street a cluster of constructions with shallow facades, very tall or very low, like a snaggle-toothed comb, seems to indicate that from there the city's texture will thicken.
But you continue and you find instead other vague spaces, then a rusty suburb of workshops and warehouses, a cemetery, a carnival with Ferris wheel, a shambles; you start down a street of scrawny shops which fades amid patches of leprous countryside.
If you ask the people you meet, ‘Where is Penthesilea?’ they make a broad gesture which may mean
‘Here,’ or else ‘Farther on,’ or ‘All around you,’ or even ‘In the opposite direction.’
‘I mean the city,’ you ask, insistently.
‘We come here every morning to work,’ someone answers, while others say, ‘We come back here at night to sleep.’

To identify the urban, to understand and give it a form is, ultimately, the real challenge for contemporary architecture. Rem Koolhaas was perhaps the first to understand this: ‘In 1995 I started teaching at Harvard. I wanted to call my programme Study Centre of (what was once) the City, but the faculty believed that my proposal was too radical.’5 By 2006 architectural historian Richard Ingersoll could declare in his Sprawltown (2006)6 that the urban is an unavoidable reality of modern life — a reality that we should take seriously, and recognise as a new terrain for possible urban design. To rethink the urban means therefore to recognise, first and foremost, its ambiguous character; but it also means to acknowledge its scalar complexity. If on the one hand the logic of the urban is deployed at the scale of the relationship between built space and the networks or systems traced on a territorial level, then on the other hand the urban has profound repercussions on a smaller scale – the scale of the continuities and the discontinuities that mark urban space as well as the relationships between citizens and their living space.

Since the second half of the twentieth century, we have become used to measuring and quantifying the urban. In fact, we define what can be considered urban on the basis of the consistency of its built mass, and on the number of its inhabitants. In France, since 1954 the nomenclature of unité urbaine or urban agglomeration is defined as a continuously built area marked by voids less than 200 metres wide, and hosting at least 2000 inhabitants. Clearly, the number of inhabitants is no longer – and for some time has not been – the single meaningful criteria to define what is a city, and is even less useful to define the urban.

Beyond the simple question of its spatial qualities and of its territorial placement, the urban is a transversal research topic, characterised by a range of sociological, economic, anthropological, political and historical questions. Processes of urbanisation are fundamental in the shaping of the choices of billions of individuals who migrate or settle, change habits or embrace a culture, see their futures change or their past rewritten depending on the strength of local policies – or of the lack thereof.

While the city – or at least most cities – develops due to the strategic or symbolic relevance of its geographic location, the Urban follows a networked logic, the logic of the distribution of water, services, and energy. The urban is a molecular, aggregative form that is marked both by an essential continuity – the continuity of transport connectivity – but also by moments where social and economic asymmetries manifest themselves through radical heterogeneity in density and form. These moments of discontinuity are the mirror of profound territorial and cultural processes, and they are perhaps the first parameter we could use, as architects, to observe and compare the evolution of the urban in different contexts. It is perhaps only by highlighting the specificity of the processes that created what we could call the

‘socio-spatial’ form of Brooklyn, in the Greater New York area, that we can learn, by contrast, to understand better the social evolution of Paris and London. Researching these discontinuities also means to rethink the relationship between spatial organisation and socio-economic processes – a relationship that is often anything but linear. Studying the effects of segregation, gentrification, and mobility, as well as the political role of physical and perceived barriers is today more than ever a fundamental step towards a better understanding of the urban as a phenomenon.

Understanding the urban has become an urgent task for architects as it is perceived as ‘the most radical expression of the anthropization [sic] of the environment.’7 The debate on climate change highlights in an increasingly clear manner some of the effects of urbanisation, such as the pollution of air and water, and the impoverishment of the arable land devoted to food production. The urban can therefore be considered the hallmark of the Anthropocene, that is to say the age – in the geological sense of the term – when the impact of society on the environment becomes so intense as to affect it in a permanent manner.

Up until today, the presence of a service network has been the sine qua non of the development of the urban condition. Energy, water, and transportation, enabled the sprawling of cities into much broader urbanised areas. These service grids constructed the landscapes of modernity much in the same way in which rivers shaped pre-modern territories – but it is precisely these grids that we might question today, in order to face the ecological challenges posed by the urban. Today, the possibility that some urbanised areas might not have to be served by a system of centralized networks seems increasingly plausible. Examples of ‘post-network urban’ terrains emerge as alternatives to a diffuse suburbia; these alternatives rearticulate the relationship between centralised infrastructures and local systems, and in doing so suggest the possibility of the emergence of new urban figures.

Already since the 1990s, for instance, the town of Woking, situated 45 km from London, has been at the avant-garde of research in renewable energy. The city administration has initiated a project aimed at the local production and distribution of energy, and promoted forms of autonomy from the national grid. Similarly, in the Stockholm archipelago 100,000 residential units are not connected to the national water and sewage network. In the largest municipality of the region, Norrtälje, 45% of the population lives beyond the reach of centralised infrastructure. These two examples show that the post-network scenario is an actual reality. Its emergence implies potential mutations in the urban metabolism and in the ways in which the flux of environmental resources is crystallised – through architecture – into a process of urbanisation.

Woking and Norrtälje also highlight the fact that in the contemporary political economy and ecology of urban services, what matters is the is the movement of matter and energy, rather than the presence of fixed infrastructure. Less optimistic but equally striking examples can be seen in developing countries. In many African cities, the patchy quality of national infrastructures has triggered the rise of commercial service providers – be they individual or collective, formal or informal, quite often illegal vis-a-vis the theoretical exclusivity of the contracts that citizens should respect as opposed the state operators who should officially be in charge of these services. As Sylvy Jaglin has observed, ‘these offers compensate the deficiency of conventional services and cater to clients who are excluded from the provision of services due to their economic status, their geographic isolation, or their lack of legal citizenship.’ 8

The sociopolitical implications of the post-network urban terrain are quite ambiguous; more thorough theoretical and empirical research will be necessary if we want to make sense of the often-contradictory logic that underpins this scenario. The post-network urban is at the same time an infrastructural strategy, an analytical category, a progressive alternative, a possible ecological solution, but also a spatial process that reconfigures the fragmentation of the urban in new ways. This emerging systemic process will change the very definition of the word urban, once more.

After all, one of the most interesting qualities of words is their ability to change meaning. The urban – and its attendant ‘urbane’ – has encapsulated for centuries an idea of savoir vivre as characteristic of the (European) city dweller. And yet, in New York during the early 1970s, a new cultural phenomenon interpreted the post-industrial condition in a way that would shift the meaning of the word ‘urban’ again: hip-hop.

Initiated by young African-American, Caribbean, and Latino inhabitants of the South Bronx hip-hop was made popular by the founder of the Universal Zulu Nation, Afrika Bambaataa. In 1974, the new programme director of WBLS radio Frankie Crocker

‘Holliwood’, a DJ from Buffalo, invented the expression

‘contemporary urban’ to define the eclectical mix of songs he played on air. Crocker’s expression popularised the use of the term ‘urban’ as a less historically charged alternative for ‘black’.

Hip-hop spread from the US to Europe in the early 1980s, becoming particularly prominent in the UK and France. ‘Urban culture’ became the culture of the Parisian banlieues at a time when the introduction of the suburban rail network RER allowed unprecedented connectivity between centre and periphery.9

From urbane to hip-hop urban, it is ultimately the citizens who define what is the meaning and value of living in a city. And yet, architecture can still be a space of experimentation where these meanings and value are tested and recast into new, alternative scenarios.