Sioux invocation. Sanctuaries are most often large boulders of rolling stone or other rocks that [...] were charged with mythical significance. Priests and warlords went there to invoke the help of supernatural powers. The large block of stone on which this supplicator stands would have the power to reveal to the warrior the outcome of the raid he is planning. Its surface carries what the Indians call the footprint of the human foot and it is to this particularity that it must have become sacred. Photo taken from volume 3 of Edward S. Curtis's encyclopedia (1868-1952) on North American Indians; with a foreword by Theodore Roosevelt. Between 1907 and 1930; 20 volumes were published.