The will to develop and expand Algiers which is a city with a deep history and a nice geographic location in the north African coast always has been an ambition for different architects and urbanists through time especially during the colonial period, in this paper, that ambition can be seen in the plan proposed by Le Сorbusier. After his visit in 1931 to Algiers, the Corbusier took it upon himself to design a plan for a future Algiers, He called it Plan Obus. This paper discusses the importance of taking care of heritage areas like ''The Casbah''  in any development strategy proposed , and which role did they play in the case of plan Obus , we will see also the real intention of Corbusier of proposing this future plan of Algiers which is the first  of its kind , the paper aims also to see the  Obus plan from a  Sustainable development view and if it matches with the  Sustainable development pillars nowadays , and what are the causes which made this mega project not realizable and far from to be built.