The historic center of Gerace, in Calabria, southern Italy, can be considered a perfect case study for investigating the relationships between transformations and preservation. Tansformations should not be seen as a loss of authenticity for architectural heritage: they may represent a tangible trace of the times and the natural evolution of an urban settlement. Trying to preserve this complexity represents a great challenge in terms of seismic vulnerability evaluation. Each past intervention complicates the level of knowledge accumulated that Italian guidelines for the assessment and reduction of seismic risk of cultural heritage define to estimate the structural safety of historical buildings. The present paper aims to explore the idea that every design choice, especially if regarding structural interventions, should arise from a profound knowledge of the pre-existing architecture.