French iconographer of medieval sculpture and decorative arts. Cahier studied at the College of Saint-Acheul. He joined the Jesuit order, ordained as priest, in 1824. Cahier lectured at the Jesuit colleges in Paris, Brieg (in the Swiss Canton of Wallis), Turin, and in Belgium at Brugalette. In the pre-photography days, Cahier began "collecting" medieval monuments, noting their location and iconography with the idea of documenting the Christian (i. e., Roman Catholic) faith via art of the middle ages.