When the first Spanish missionaries penetrated the Chaco early in the seventeenth century, they discovered a whole group of linguisticallyrelated tribes whose existence had gone unsuspected for a century. The most important of them, the Mataco, numbered about 30,000, and lived in numerous villages along the banks of the Bermejo, Paraguay, and Pilcomayo rivers. Pushed down off the Bolivian highlands by the more warlike Chiriguanos, the Mataco lived a peaceful, if primitive, life, hunting, fishing, and collecting carob pods, cactus figs, wild squash, and hearts of palm. During the eighteenth and nineteenth centuries, while Argentina exterminated most of her Indian population, the Mataco were left practically undisturbed; their lands were simply not valuable enough to be worth the white man's taking. Except for a few Anglican missions and an occasional trading post, the Chaco remained sealed off from the rest of Argentina.