The essay, by using documents and historical sources, suggests a new analysis of illegal housing development in the building of Roman suburbs during the period of Fascism. The analysis describes the political and legal debate set off by the liberal government before Fascism and later on during the regime to come up with a definition of "illegal housing development" and in order to control this process in the suburbs. The essay aims to propose an historiographical consideration to review the definition of "illegal housing development" during Fascism and before the planning law of 1942. It suggests that different forms of housing developments, adopted by many private companies and building managers and defined as "illegal processes" after Fascism, now can be considered a "self-made process". The analysis aims to be useful in reviewing the different forms of urban expansion during the regime and in understanding the effects of building policies on development of suburbs in Rome.