The Sun Dance was one of the most important religious events for some plains tribes, especially, but not limited to, the Sioux and Cheyenne.  The ceremony was not a part of a pre-scheduled happening but was given by a leader or warrior at their request to fulfill a promise or to seek help for an important change of situation.  It was a test of young men by ordeal in which long thongs suspended from a central pole are fastened through the skin of their chest and the participants danced around the pole in prayer blowing on an eagle wing bone whistle and pulling back away from the pole until the thongs tear the skin and pull free.  Because of the influx of Non-Indians in attendance  to watch, the tribes do not allow participation by anyone who is not Native and filming is prohibited.  The ceremony, because of the self-torture, was prohibited in both the U.S. and Canada in the late 18th century.  Canada allowed it to continue in 1951 and the U.S. in 1978.  Native tribes, through their leadership, popular activism, and appeal to Governments, have sought to keep the Sundance from public eyes in hopes that future generations may know and learn from the rites and beliefs of their ancestors.