Interested in medieval art, Barnard gathered discarded fragments of medieval architecture from French villages before World War I. He established this collection in a church-like brick building near his home in Washington Heights, Manhattan in New York City. The collection was purchased by John D. Rockefeller Jr. in 1925 and forms part of the nucleus of The Cloisters collection, part of the Metropolitan Museum of Art. At least one object, sold to the Museum of Fine Arts, Boston in 1924, he offered with misleading provenance.