The Byzantine legacy in modern architecture can be divided between a historicist, neo-Byzantine architectural style and an active investigation of the potentials of the Byzantine for a modern, explicitly nontraditional, architecture. References to Byzantium in avantgarde Eastern European architecture of the 1920s employed a modernist interpretation of the Byzantine concept of space that evoked a mode of “medieval” experience and creative practice rather than direct historical quotation. The avant-garde movement of Zenitism, a prominent visionary avant-garde movement in the Balkans, provides a case study in the ways immaterial aspects of Byzantine architecture infiltrated modernism and moved it beyond an academic, reiterative formalism. By examining the visionary architectural design for the Zeniteum, the Zenitist center, in this article, I aim to identify how references to Byzantium were integrated in early twentieth-century Serbian avant-garde architecture and to address broader questions about interwar modernism. In the 1920s, architects, architectural historians, and promoters of architecture came to understand the Byzantine concept of space in ways that architects were able to use in distinctly non-Byzantine architecture. I will trace the ways Zenitism engaged the Byzantine architectural construct of total design, in which structure joins spirituality, and related philosophical concepts of meaning and form derived from both Byzantine and avant-garde architecture. This reassessment of Zenitism, an Eastern European architectural movement often placed on the margins of the history of modern architecture, has broad implications for our understanding of the relationship between tradition and modernism.