Auguste Longnon’s interest in the national territory, in historic Gaul and in France, helped to popularise historical geography. He joined the Commission de Topographie des Gaules (CTG) in 1869. The subject of his writing, between 1871 and 1914, following the fall of the Second Empire, is representative of the period as a whole, characterised by intense reflection on the idea of the nation and the borders of France. In the Atlas, he pays tribute to the work of his mentor, Alfred Maury, and to the work of the CTG more generally. The CTG had given him access to all their documentation, which he used for his work.