The Eixample district of Barcelona gained notoriety as an “architectural playground” in the early 20th century. Behind the design of the Eixample district was the Catalan civil engineer Ildefons Cerdà. Rather than continue the haphazard urban dynamic of the old city, Cerdà proposed an extension that spread out the urban fabric; implementing 113m square chamfered blocks and introducing shared space into the public realm. Almost 70 years later, Le Corbusier, after making a name for himself as an architect, began to develop his theories in urban design and planning. Shortly after his seminal work Ville Radieuse, Le Corbusier designed the Macià plan for Barcelona, one that directly implemented his urban theories, while simultaneously acknowledging and challenging the physical manifestation of Cerdà’s Eixample extension. This paper will examine how Le Corbusier’s Macià plan serves as both an understanding and questioning of Cerdà’s plan and an early implementation of Le Corbusier’s modernist planning. Specifically, this paper will look at the similarities in design between the two plans, the challenges Le Corbusier proposes in contrast to Cerdà’s plan, and the physical insertion and connection between the Macià plan and the Cerdà plan. This paper will consult the original plans and documents of both Cerdà and Le Corbusier, specifically referencing the Foundation le Corbusier and GATEPAC as primary sources, to directly examine each of the planner’s theories behind their proposal. Furthermore, the Athens Journal of Architecture will provide insight into the relationship of the plans, specifically investigating how Le Corbusier questions Cerdà’s urban plan.