The research problem lies in the insufficient development of the concept of protomediality – a phenomenon that connects material forms of dwelling with the emergence of the public sphere. The relevance of the topic stems from contemporary transformations of communication: digital platforms are turning from channels of information exchange into spatial environments that shape social relations and identities. The article proposes, for the first time, to interpret the prehistoric dwelling and the cult hearth as historical mediators of social interaction that predetermined the architecture of urban and digital public spaces. The novelty of the approach consists in combining cultural-anthropological, spatial-semiotic, and media-theoretical analyses to reveal the origins of publicness within spatial practices of collective existence. The results demonstrate that protomedial structures – house, hearth, agora – formed mechanisms of social communication later reproduced in institutional and digital forms. The conclusions emphasize that the spatial organization of communication was medial in its very nature, and that contemporary digital platforms represent a continuation of this ancient logic: they function as environments of social co-presence, where publicity arises not from message transmission but from shared being-together.