To know is to name, according to Jean-Louis Le Moigne, the author of the Théorie du système général. Starting from a desire to transpose the genetic method to architecture, the necessity to create the word « ante-project » has become clear; which has revealed one of the differences between literary genesis and architectural genesis : the role of the order and of context. This role will be illustrated through the study of the genesis of the residential block at number 20-28 rue Ramponneau in Belleville, designed by Fernando Montès, and more precisely the study of the transformations of the reference which has worked as the prime mover of this genesis : Casa Rustici by Giuseppe Terragni.