This paper investigates fourteenth-century accounting sources, in order to draw deductions - necessarily presumptive - on the themes of vulnerability, collapse and reconstruction of medieval structures. The case-study and its context are taken from accounting sources produced by the administration of the princedom of Savoy-Achaia, a subalpine appanage established in 1295: materials, workers and construction processes are documented by various ordinary and extraordinary accounting instruments. The building considered is the turris magna de medio (the big central tower) of the castrum of Pinerolo, which collapsed in August 1319 and was rebuilt in the following years; this element was the pivot of the castle, which had been transformed into the main seat of the prince a few years before. The analysis of the accounts leads to the identification - in a conjectural way - of vulnerabilities linked to the administrative procedures, the techniques chosen and the building processes adopted. Il saggio discute il crollo di una torre sabauda nel 1319, analizzando le fonti contabili relative al cantiere e le fonti iconografiche di età moderna, avanzando alcune ipotesi sui diversi tipi di vulnerabilità sottesi all'evento, e discutendo le modalità di migliore ricostruzione dell'edificio.