Not for the first time I felt myself confronted by the dizzying possibility that an entire episode in the story of mankind might have been forgotten. Indeed it seemed to me then, as I overlooked the mathematical city of the gods from the summit of the Pyramid of the Moon, that our species could have been afflicted with some terrible amnesia and that the dark period so blithely and dismissively referred to as `prehistory' might turn out to conceal unimagined truths about our own past. What is prehistory, after all, if not a time forgotten--a time for which we have no records? What is prehistory if not an epoch of impenetrable obscurity through which our ancestors passed but about which we have no conscious remembrance? It was out of this epoch of obscurity, configured in mathematical code along astronomical and geodetic lines, that Teotihuacan with all its riddles was sent down to us. And out of that same epoch came the great Olmec sculptures, the inexplicably precise and accurate calendar the Mayans inherited from their predecessors, the inscrutable geoglyphs of Nazca, the mysterious Andean city of Tiahuanaco ... and so many other marvels of which we do not know the provenance. It is almost as though we have awakened into the daylight of history from a long and troubled sleep, and yet continue to be disturbed by the faint but haunting echoes of our dreams