In the beginning of the 19th century, the Apiacá tribe consisted of nearly 16,000 people. In 1812, one settlement consisted of around 500 people in which half were warriors. They were once a large tribe until the rubber boom took over Amazonia. The rubber boom also pushed and scattered the Apiacá away from their historical territory. The Apiacá had a strong fighting culture. They often fought with their nearby competitors, such as the Tapanyuna tribe, located on the rightward side of the Arinos River. However, the Apiacá did not fight for materials, but instead to avenge past conflicts. With around 200 to 300 warriors, every year they would march to battle against another tribe. Apiacá would also practice cannibalism to their prisoners. Throughout the existence of the Apiacá, their numbers have declined dramatically. Because of the establishment of the "Collectoria estadol do Mato Grosso" in 1912, many were killed and 32 remained. They were killed in compensation from an attack they made at the collector’s office. In 1916 there was evidence of some black people having been assimilated into the tribe.