... reported large, well-populated cities on the Amazon flood plains, modern archeologists have generally traveled to the high Andes for "high" ancient civilizations in South America. In retrospect, this is not surprising. By 1700, the cities of the 1540s had been swallowed up by the jungle. Besides, most thought, the conditions in the lowland tropics are too harsh to nourish advanced societies. Fortunately, a few archeologists have recently invaded Amazonia with aerial sensors, magnetometers, and the oldfashioned shovel. And indeed there once was a high civilization along the great river; and, some say, it may have spread from the lowlands to the Andes far to the west. What a turnabout in archeological outlook -- if sustainable by facts. One intriguing site in Amazonia is the island of Marajo, 15,000 square miles in area, located at the mouth of the Amazon. Here are found some 400 huge dirt mounds, including one with a surface area of 50 acres and a volume of a million cubic yards. Radiocarbon dates suggest that Marajo had been occupied for over a thousand years. Nearby, on the Tapajos River in Brazil, A. Roosevelt found elaborate pottery, finely carved jade, and a culture going back perhaps 7,000 years. In other parts of Amazonia, surveys uncovered tens of thousands of acres of raised fields connected by causeways. There remains little doubt that an advanced, complex civilization dwelt in Amazonia for millennia. Archeologists are now asking where these people came from and how they were related to the Incas to the west and civilizations to the ...