<P> Shell mounds were the earliest evidences of habitation; they represent piles of human refuse and are mainly dated between 7500 and 4000 years BP . They are associated with ceramic age cultures; no preceramic shell mounds have been documented so far by archaeologists . Artificial earth platforms for entire villages are the second type of mounds . They are best represented by the Marajoara culture . Figurative mounds are the most recent types of occupation . </P> <P> There is ample evidence that the areas surrounding the Amazon River were home to complex and large - scale indigenous societies, mainly chiefdoms who developed large towns and cities . Archaeologists estimate that by the time the Spanish conquistador De Orellana travelled across the Amazon in 1541, more than 3 million indigenous people lived around the Amazon . These pre-Columbian settlements created highly developed civilisations . For instance, pre-Columbian indigenous people on the island of Marajó may have developed social stratification and supported a population of 100,000 people . In order to achieve this level of development, the indigenous inhabitants of the Amazon rainforest altered the forest's ecology by selective cultivation and the use of fire . Scientists argue that by burning areas of the forest repetitiously, the indigenous people caused the soil to become richer in nutrients . This created dark soil areas known as terra preta de índio ("indian dark earth"). Because of the terra preta, indigenous communities were able to make land fertile and thus sustainable for the large - scale agriculture needed to support their large populations and complex social structures . Further research has hypothesised that this practice began around 11,000 years ago . Some say that its effects on forest ecology and regional climate explain the otherwise inexplicable band of lower rainfall through the Amazon basin . </P> <P> Many indigenous tribes engaged in constant warfare . James Stuart Olson wrote: "The Munduruku expansion dislocated and displaced the Kawahíb, breaking the tribe down into much smaller groups...(Munduruku) first came to the attention of Europeans in 1770 when they began a series of widespread attacks on Brazilian settlements along the Amazon River ." </P> <P> In March 1500, Spanish conquistador Vicente Yáñez Pinzón was the first documented European to sail up the Amazon River . Pinzón called the stream Río Santa María del Mar Dulce, later shortened to Mar Dulce, literally, sweet sea, because of its fresh water pushing out into the ocean . Another Spanish explorer, Francisco de Orellana, was the first European to travel from the origins of the upstream river basins, situated in the Andes, to the mouth of the river . In this journey, Orellana baptised some of the affluents of the Amazonas like Rio Negro, Napo and Jurua . The name Amazonas is taken from the native warriors that attacked this expedition, mostly women, that reminded De Orellana of the mythical female Amazon warriors from the ancient Hellenic culture in Greece . </P>

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