Scarcely fifty years ago the “Indian sphinx” posed enigmas that seemed simple. Known pre-Columbian civilizations were relatively few, and their past, however obscure, could be considered recent in contrast to the millenniums that separate us from the cultures of the ancient Orient. Today this is no longer true. The emergence of new archeological horizons has singularly transformed our summary view of the history of man in the Western Hemisphere. The date of the first human migrations through the Bering Straits has been put back some twenty or thirty thousand years—to the Aztec, Mayan, and Incan civilizations which the Spaniards knew in their full flower. Others have been added which, in turn, give rise to fresh enigmas.