Francois Amelinckx (Amelinckx n.v.) and Jean Florian Collin (Etrimo) were two Belgian pioneering developers who started their activities in the interbellum period and in the decades following WWII able to briefly dominate the residential real estate market. Together they produced more than 70.000 apartment units, housing the population of an entire ‘invisible city’. Their activities cover large portion of the twentieth century (from the 20s to the late 70s) and echo structural transformations that occurred during that period. Through the detailed analysis a selection of their projects, it is possible to build a profound understanding of the role developers played in shaping the urbanization of the metropolitan area in the middle of the twentieth century. More specifically, this research project will analyze the interplay between the urban context (infrastructure and access to land), the urban and architectural models that where applied, and the legal and policy frameworks that regulated commercial residential development. Through a series of case studies, the project will build an understanding of these development practices and at the same time render concrete the type of urban environment these actors produced. The project seeks to substantiate and test the hypothesis that the metropolitan ambitions of these real estate pioneers have been stalled in the post-war period and that this had lasting consequences for the way in which urban project development could develop in Belgium.