The accelerating pace of global urbanisation is reshaping planning agendas toward integrating urban nature, yet dominant approaches continue to rely on designed or controlled interventions to produce engineered approximations of spontaneity. This study presents Rome as a striking example of spontaneous urban nature, where wild flora has reclaimed ruins, walls, and neglected spaces for centuries without planned intervention. By “wild” or spontaneous vegetation, this paper refers to unmanaged, self-seeding flora that establishes itself without deliberate planting, irrigation, or maintenance, colonising ruins, walls, abandoned lots, and urban margins through autonomous ecological processes. The paper adopts a critical narrative synthesis methodology, integrating historical–cultural evidence, contemporary ecological data drawn from peer-reviewed biodiversity surveys within Rome’s urban boundary, and a spatial analysis of georeferenced historical cartographic sources to build an interpretive framework for what is here called passive coexistence. The key findings demonstrate that Rome’s sub-Mediterranean climate and centuries of aesthetic conditioning through visual arts, literature, and film have together produced a tacit social acceptance of spontaneous vegetation, effectively substituting for the deliberate education campaigns and designed interventions required in comparable cities. The study proposes an alternative narrative of spontaneous urban nature, guided by ecological monitoring and grounded in heritage planning frameworks. Despite context-specific limits, Rome’s passive coexistence paradigm offers a provocation and existing proof for more-than-human cities that seek resilience without the resource burden of engineered green infrastructure.
Martella et al. (Mon,) studied this question.