During the Middle Ages, the relationship between the neighbour principalities of Dauphiné and Savoy influences the evolution of a huge territory stretched between Lake Geneva, the Mediterranean Sea, the Rhone Valley and the Padan Plain. Their common History, however, is far from being fully known. Castles, which are, because of their many functions, the very heart of the medieval society, seem to be the key to understand it. Through the study of the castles and castellanies of Montluel, Moras-en-Valloire, Sallanches and Queyras, based on series of account rolls and registers kept by the two administrations, it is possible to analyse the evolution of the space mentioned above, from the mid-13th century to the late 15th century - a period of time during which Dauphiné became united with France (1349) and the county of Savoy was made a duchy (1416). Facing such changes, the ways of princely power deeply evolve, outlining what will later become known as the modern state.
