Within just three years, he had assembled the largest collection of Rodin's works outside Paris, including bronze castings, plaster studies, drawings, prints, letters, and books. In 1926, Mastbaum commissioned French architects Paul Cret and Jacques Gréber to design the museum building and gardens. Unfortunately, the collector did not live to see his dream realized, but his widow, Etta Wedell Mastbaum honored his commitment to the city, and the Museum opened on November 29, 1929.