Abstract:The article is an exploration of urban imaginaries emerging through a play with materials. Starting from a complex activist exercise for reimagining the space of a park in decay, whose protagonists are children, we propose a reflection on the productivity and resilience of matter. We argue that a new materialist sociology is one that takes disappearances seriously. Capitalism renders space abstract not only through flow and circulation, but also through stillness. We follow the curious disappearances and reappearances of the park in question, tracing the mutations of urban planning, of the juridical domain, and of the everyday use of space. Finally, we analyse the making of a maquette of the park by a group of children and their alliances with activists. The maquette is a political "thing": it leads us away from an urban imaginary populated by discrete objects to an urban imaginary of depth and it reconcretises space. Key words: children's imaginaries, radical social imaginaries, new materialism, children's participation.3 Introduction In his writings Althusser (2006) insisted that materialism is the most difficult problem that we encounter as social thinkers. We here propose a sociology of disappearances and reappearances, as part of a new materialism of the encounter. Things are not static, but they are in constant movement. Things leak out of themselves. Things leak into invisibility. The new materialist sociology we argue for is one that takes disappearances seriously.In the past two decades, a creative place of utterance has emerged in critical urban scholarship: it is a place defined by surpassing a firm opposition between poststructuralism (which has tended to dispense with things) and Marxian phenomenology (which has tended to substitute things for objects, and to argue that we have lost the thingness of things to objects). The productivity and the resilience of matter became the most important materialist story to recuperate (Coole and Frost 2010). Matter returned, but in its processual insistence, as matter that becomes, rather than as matter that is.To this discussion, we add two peculiar questions. How can we tell a story of a disappearance of an urban space (here, it is the space of a park) from urban imaginaries? As we show, capital accumulation turns space invisible. How does space reappear through creative alliances of children and activists around materials? By

Nature is a domain where the scientific, the capital, and the political meet, in constant negotiation and making of Nature. By Nature with a capital 'N' we mean an abstract concept of Nature as one external and in contrast to Society with a capital 'S'. While these concepts are abstracts, they are at the same time very real in that they have to be made, maintained, and are acted upon, thus shaping reality (see Latour, 2004; Moore, 2015). The result of this making of Nature is by no way fixed and is often contested as claims on the protection and exploitation of Nature are made. We understand the exploitation of Nature as embedded in a neoliberal agenda of both resource extraction and touristic attraction, while nature's protection oscillates between ascribing degrees of intervention and the exclusion of humans from other than human environments, such as what is proclaimed as wilderness. Yet on the ground, human and other than human interaction is a practice of assessment, judgement, and selection, where questions of right, of emotional attachments, and the survival and reproduction of species-human and non-human-are put to the test. While Nature often appears as a bound more than human entity, specific entities like trees, flowers, animals, mushrooms, and microbes are often invisible and uninteresting groups. They leave categories of indifference only when they become potential resources (or threats) to human lives. When not material resources, they are moralising comparisons to human socialities as mere metaphors rather than entities in their own right (Tsing, 2005: 172; see also Lorimer, 2007). We direct our interest towards those modes of assessment that happen in space and time, 'on the ground', where entities are sorted in a bid to make Nature.

Lefebvre’s 1970 prophecy of the total urbanisation of society has come true with the expansion of the urban into natural and rural territories. For Lefebvre, the question of nature is closed by its ‘steady, violent death’ (Lefebvre, 2003) and its replacement by a ‘second nature’ (Schmid, 2014; Smith, 2008). This closure accounts at an epistemic level, for the dominance of the urban (Krause, 2013; Brenner and Schmid, 2014). Far from being closed, the question of nature is renewed within the present conditions of planetary urbanisation, as the interiorised non-urban is ‘operationalised’ to sustain urban growth, thus making the non-city ‘an essential terrain of capitalist urbanisation’ (Brenner, 2016). In what follows, I present how the Romanian forest is operationalised as a territory of planetary urbanisation through forest management practices. Looking into the negotiations and manipulations on the ground provides a way to ‘pay attention’ (Stengers, 2010) to those practices that sort and select natural areas. In the face of the recorded disappearance of the forest, the effort of making visible the rationality of planning, and the challenges that are posed upon it inscribes itself within an ‘ethics of visibility’ (Roberts, 2012; Topalovic, 2016).