This paper focusses on the production of the two major commercial residential developers, Jean-Florian Collin (Etrimo) and François Amelinckx (Amelinckx N.V.), who constructed over 70,000 apartments in the metropolitan agglomerations of Belgium between 1924 and 1985. Their short-lived, but large-scale, production defines an ‘invisible city’ of which we know very little but can be used to analyse key aspects of the process of twentieth-century metropolization in Belgium. Both developers were ‘champions of a game of their creation’, as they applied precise strategies in constructing specific circumstances that seized the latent potential of development (that hovered over the capitalist metropolitan landscape) into concrete, often opportunistically defined, built commodities. By applying a production perspective on planning history, it is possible to look at the processes of metropolitan expansion and twentieth-century planning in Belgium from a different angle, starting from the actual built reality and the ‘captains of industry’ that this urban reality was grounded upon. A perspective which has been little-applied in the Belgian case, and is particularly pertinent for interpreting development patterns in a context like Belgium that lacks a strong planning culture and is historically compromised the absence of an emancipated scene of developers ready to take on the urban agenda.