This study proposes an anthroposemiotic theory of prehistoric writing, moving beyond the traditional view that script emerged purely from administrative needs in early Mesopotamian civilizations. Instead, it intends to demonstrate that writing’s deepest roots may lie within the graphic and ritual practices of the Upper Palaeolithic. Approaching early humanity as Homo symbolicus, this study explores how cave art, geometric signs, and monumental architecture may have functioned as exosomatic memory and sacred mediation. Drawing on archi-écriture and spatial syntax, the research shows that prehistoric marks organized spatial relations and structured symbolic ecosystems long before their formalization into phonetic scripts. Ultimately, writing’s genesis can be situated within a broader cognitive evolution, where symbolic exteriorization transformed natural surfaces into durable spaces of meaning.