The phrase "Our ancestors the Gauls" has long been part of the history of France to define the origins of the nation. For decades, this national novel began with the entry of these ancestors on the historical scene: smart but rowdy, joyous but heavy drinkers, brave but divided, glorious but defeated. Beyond its apparent simplicity, the expression poses many historical and epistemological problems . It is not a question of genetic but belongs to cultural history, as it conveys a particular conception of identity and nation. This is what appears when we compare the academic writings of the great historian Ernest Lavisse with his famous textbooks, the Petits Lavisse. We witness the making of ancestors in a moral and political use of history. In order to build the nation, school becomes the place where it is forged. We must therefore take an interest in shaping "Our ancestors the Gauls", and in the choices and silences of scientific and academic discourses. Ernest Lavisse, who became the symbol of the school of the Third Republic, manufactured the Gauls with his pen, in the Gallic (or Gauls) foundry of the nation, one of the major historical figures needed by the new-born Republic. This history of knowledge shows that the discourse on the nation's antique origins proves to be a speech about the present that takes the voices of the past.