Leymarie writes that "in order to illuminate the synagogue both spiritually and physically", it was decided that the twelve windows, representing the twelve tribes of Israel, were to be filled with stained glass. Chagall envisaged the synagogue as "a crown offered to the Jewish Queen", and the windows as "jewels of translucent fire", she writes. Chagall then devoted the next two years to the task, and upon completion in 1961 the windows were exhibited in Paris and then the Museum of Modern Art in New York. They were installed permanently in Jerusalem in February 1962. Each of the twelve windows is approximately 11 feet high and wide, much larger than anything he had done before. Cogniat considers them to be "his greatest work in the field of stained glass", although Virginia Haggard McNeil records Chagall's disappointment that they were to be lit with artificial light, and so would not change according to the conditions of natural light. French philosopher Gaston Bachelard commented that "Chagall reads the Bible and suddenly the passages become light." In 1973 Israel released a 12-stamp set with images of the stained-glass windows. The windows symbolize the twelve tribes of Israel who were blessed by Jacob and Moses in the verses which conclude Genesis and Deuteronomy. In those books, notes Leymarie, "The dying Moses repeated Jacob's solemn act and, in a somewhat different order, also blessed the twelve tribes of Israel who were about to enter the land of Canaan... In the synagogue, where the windows are distributed in the same way, the tribes form a symbolic guard of honor around the tabernacle." Leymarie describes the physical and spiritual significance of the windows:  At the dedication ceremony in 1962, Chagall described his feelings about the windows:  In 1964 Chagall created a stained-glass window, entitled "Peace", for the UN in honor of Dag Hammarskjöld, the UN's second secretary general who was killed in an airplane crash in Africa in 1961. The window is about wide and high and contains symbols of peace and love along with musical symbols. In 1967 he dedicated a stained-glass window to John D. Rockefeller in the Union Church of Pocantico Hills, New York. The Fraumünster church in Zurich, Switzerland, founded in 853, is known for its five large stained glass windows created by Chagall in 1967. Each window is tall by wide. Religion historian James H. Charlesworth notes that it is "surprising how Christian symbols are featured in the works of an artist who comes from a strict and Orthodox Jewish background."