This thesis proposes a theoretical framework for spatial inquiry into conditions of radical social gregariousness, through probing the crowd design problem in the work of the Soviet Rationalist architects (1920s-30s) - particularly their submissions to the Palace of Soviets competition (Moscow 1931-3). Legitimizing the crowd construct as an index of collective consciousness, and examining the early-modern revolutionary crowd's struggles for proclaiming its self-consciousness, this thesis investigates the interwar political phenomenon of amassing large crowds within buildings as a device for constructing collective social relations. The research project is divided into two main parts. The first is concerned with the crowd design problem, identifying this problem not just as the technical task of accommodating large political crowds, but as the basis of the formulation a new kind of conceptual intent in architecture. Finding the competition brief inadequate to in-depth formulation, the thesis investigates three primary sources for the crowd design problem: mass-events, revolutionary-theatre and revolutionary-art. Four components comprise the Crowd Design Problem each seeking legitimacy in the mass of crowd-bodies: i) the problem of crowd configurations; ii) challenges from the kinesthetic-space conception evoked by theatrical director V.E. Meyerhold's Biomechanics; iii) the legitimacy of 'the object' within a spatial-field of intersubjectivity; and iv) the challenge of 'seeing' crowds from immersive viewpoints counteracting representational filters of class privilege. Part-II focuses on the response of the Rationalists--one of the groups participating in the competition--to the crowd design problem. The study unearths in their designs a logic of space-making founded in the construction of inter-subjective states of consciousness radically different from prevailing individualistic conceptions of social space. To explain this logic of space-making, it proposes the notion of Gregarious Space--a theoretical framework of inquiry into what Marx called "species-being", taking radical gregariousness as the primary, generative condition of society. Besides drawing on morphological principles, social theory, historical analyses, and philosophical reflections, the notion of Gregarious Space is found to be particularly amenable to design propositions. Within the proposed theoretical framework, the Rationalists' design-proposition of curved-grounds, dense notations, textured co-visibilities and empathetic graphic conventions - all comprise a founding spatial-principle trafficking in rhythmic fields between subjects and against non-commodified objects: a principle which challenges the material domain of Productivist Constructivism as well as Historical Materialism's canonical constructs of alienation. Moreover, its uncertain kinesthetics sustain dynamic, aleatory states of consciousness which subvert prevailing disciplinary techniques of Panopticon inspection.