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But scientists now believe that instead of stone-age tribes, like the groups that occasionally emerge from the forest today, the Indians who inhabited the Amazon centuries ago numbered as many as 20 million, far more people than live here today.
Michael Heckenberger of the University of Florida has found moats, causeways, canals, the networks of a stratified civilization that, he says, existed as early as A.D. 800. In Bolivia, American, German and Finnish archaeologists have been studying how pre-Columbian Indians moved tons of soil and diverted rivers, major projects of a society that existed long before the birth of Christ.