Amid today’s environmental challenges, the long-standing Western divide between nature and culture is increasingly being called into question. Roman Antiquity, a significant period in our past, helps us reconsider such opposition. For the Romans, maintaining a harmonious relationship with ‘nature’ was essential to sustaining order and prosperity, as it was not a mere physical environment, but a subversive force, a realm intertwining the sensory with the divine. The use of real and iconographic vegetation in the living spaces was a central concern. The VegArch project aims to explore this vegetalisation within the specific context of Gallo-Roman sanctuaries of the 1st-3rd c. AD. From the penetration of Italic traditions to an unprecedented ‘hypervegetalisation’ of architecture, this greening has long been explained by a presumed persistence of Celtic naturalism or a mere decorative trend. Its role in shaping the experience of nature, the cosmos, and the divine can now be addressed with the expanding archaeological data and ecofacts and through an interdisciplinary approach. The vegetal forms will be gathered and compared in a trans-medial analysis, considering real and artificial forms as one and the same vegetal art and the sanctuary as a unitary system. This formal step will highlight the specificities of Gallo-Roman contexts in a global/local perspective. Through comprehensive and contextualised case studies, the vegetal forms will then be analysed in their spatial, temporal and sensory dimensions to reveal their polysemic value and how they engage the senses and shape the experience of the sacred. The resulting synthesis will contribute to the cultural history of vegetalisation of Western architecture, helping to unveil the relationship with nature in ancient societies, questioning our own practices and beliefs. The VegArch project, for which ENS is the ideal institution, will open numerous new perspectives and foster long-term European collaborations.