By the early 1940s, the foundation had accumulated such a large collection of avant-garde paintings that the need for a permanent building to house the art collection had become apparent. In 1943, Guggenheim and Rebay commissioned architect Frank Lloyd Wright to design the museum building. Rebay conceived of the space as a "temple of the spirit" that would facilitate a new way of looking at the modern pieces in the collection. In 1948, the collection was greatly expanded through the purchase of art dealer Karl Nierendorf's estate of some 730 objects, notably German expressionist paintings. By that time, the foundation's collection included a broad spectrum of expressionist and surrealist works, including paintings by Paul Klee, Oskar Kokoschka and Joan Miró. Guggenheim died in 1949, and the museum was renamed the Solomon R. Guggenheim Museum in 1952. The foundation expanded its display activities with a series of traveling exhibitions.