A voyager, he traveled throughout Europe, Greece, Macedonia, the Balkans. He was the author of numerous books on Byzantine art. In 1930, in collaboration with Louis Bréhier, he led an archaeological mission to Mount Athos. He founded the series "Archives d'Athos" at the College de France, under the patronage of the Academie des Inscriptions et Belles-Lettres and the Academy of Athens.
