61 Our Predecessor of happy memory, Pius XI, in the Jubilee Year 1925, ordered a great missionary exhibition to be held; he described its striking success in the following words: "It seems almost a miracle, which gives us a new experimental proof of the vital unity and harmony of the Church of God among all nations. . . Indeed the Exhibition was and still is like a mission encyclopedia."
Source: Evangelii Praecones (Vatican.va)