This paper stems from long­lasting research dedicated to urban risk reduction through a planning approach. It focuses on public space, proposing an inversion of the usual perspective: instead of considering public spaces for risk mitigation and urban redevelopment, here the imperatives of environmental safety and urban resilience can be instrumental for exploring the meaning and role of the public space from a different, rather compelling point of view. One starting point is the concept of SUM, Strategic Urban Structure (or Framework), from the Italian “Struttura urbana minima”, which has been introduced in order to set out the contents of urban risk reduction in local administration agendas and particularly into ordinary planning processes. The SUM has been conceived both as an analytical and a normative/planning tool. Public spaces are the backbone of both urban structure and of the SUM. From their features, localization, distribution within the
settlement, and their systemic characters, largely depend the capacity of a town to positively react to a seismic event. Six case­studies of small and medium­size historic towns in the Umbria Region (one of the many Italian Regions with a high level of seismic risk), help to understand the complexities and problems related to seismic prevention within historical centres, and the conflicts between conservation of the heritage and the imperatives of environmental safety. In order to overcome possible criticalities identified in a SUM, it is necessary to provide alternatives to its functioning through redundant elements. The concept of redundancy, which is strictly related to that of uncertainty, is very interesting and promising in this field of research.