Beginning in 1903, Marcel Poëte served as the Historical Library's director. During his tenure as director, the library began to focus on collecting documents from Parisians' daily lives and on annual exhibitions. Poëte was a historian of urbanism, a teacher, and a lecturer, a background that led him to transform the Library into an Institute of History, Geography and Economy whose subject was the urban character of the City of Paris. He wrote a volume devoted to Paris for a collection published in 1926 by the Carnegie Endowment for International Peace, the Histoire économique et sociale de la Guerre mondiale [Social and Economic History of the World War]. In a second part, the Institute's co-founder, Henri Sellier, and A. Bruggeman, also an urbanism expert, created an accurate portrait of the economic life of the capital during the war. In a second article, Physionomie de Paris pendant la guerre [The Physiognomy of Paris during the War], Marcel Poëte provided an overview of the city's history during the war years. The article blended the sensitivity of an eyewitness present during throughout the events with the more analytical vision of a historian on the Library's document collections, which can be consulted and viewed today in light of his essay.