Medievalist art historian, particularly the Romanesque, and theorist. Focillon's father was the engraver and occasional salon reviewer Victor-Louis Focillon (1849-1918). The younger Focillon grew up amidst the artists Edouard Vuillard and Auguste Rodin and the early documenter of Impressionism, Gustave Geffroy. His early schooling was in Paris at the Lycée Charlemagne and Lycée Henri IV. As a young man he helped Geffroy write first volume of Geffroy's series Les Musées d'Europe (The Museums of Europe) in 1900.