Behind the common term «traditional architecture» lies an unsuspected difficulty. What precise definition should be given? Without going so far as to give a general definition, defining traditional architecture, even at the level of a single town, is not an easy task. We limited ourselves to Beauvais, but this approach could be extended to any other town. When you ask people in Beauvais, their current perception of traditional buildings varies from one inhabitant to another. Broadly speaking, it can be summed up by saying that it is a group of common buildings of non-monumental architecture, characterised by the use of «old» materials and built before the Second World War. In the imagination, their method of construction would have remained unchanged for centuries until the abrupt break in the reconstruction of Beauvais following its destruction in 1940. However, a study of ancient iconographic and textual sources shows that what is perceived as traditional has, in reality, a limited permanence over time. Beauvais underwent several periods of metamorphosis that are only documented from the end of the 15th century onwards. Common buildings have undergone constant change as a result of involuntary destruction as well as changes in society, the economy and the environment. Each era has defined its traditional architecture in relation to emerging modern architecture. In the end, it is characterised by the way in which the past, often in the process of disappearing, is viewed and interpreted in the light of our contemporary criteria. It is not the representativeness of a building that defines it as traditional, but its preservation through the ages. Once considered as a heritage object, any building, even if it was an exception, becomes part of our identity and a reference to follow. The present object then defines the tradition of contemporaries. Traditional architecture is ultimately a constructed image, an interpretation of the past that is important because it creates identity.