There are many historical inaccuracies in this film if one considers it based on de Vaca's letter to the King of Spain detailing his ordeals and adventures. Having read Haniel Long's amazing little book on the subject in which he imagines another letter from de Vaca to the king after de Vaca has been back in Spain for some time in which he tries to convey the sense of what is "civilized" and what is "savage," I not only appreciate what the makers of this film were trying to say, but consider it a masterpiece.
Another source is the famous Lord Buckley beat monologue of the 1950's called "The Gasser" about Cabeza de Vaca. That great old hipster also homes in on the essential truth about de Vaca's letter to the King: that there is a power, for healing and compassion, which is suppressed in civilized society and which, if not used, "recedes from us." This is the message of the film, and if some characters and situations and even whole tribes were invented, it is dramatic license in the service of a great theme.
