The Trombetas and its neighbor the Erepecuru run north out of the Guiana Shield into the Amazon, and both are broken by cataracts a short way upstream. Those rapids were the point. Through the eighteenth and nineteenth centuries, people fleeing plantations and estates on the lower Amazon poled and portaged past the falls into country that slave-catchers found expensive to enter. The settlements they founded were called mocambos, and they lasted, growing Brazil nuts, fishing, farming cassava on the high ground and moving with the flood. When abolition finally came in 1888 it changed the law without changing the land. The communities kept living where they lived, unrecognized on paper, for another century.

Oriximina now contains one of the largest expanses of titled quilombo land in Brazil: five formally recognized territories covering 361,800 hectares of rainforest. Roughly ten thousand quilombola people live in the municipality, alongside about 3,500 indigenous residents, spread across a dozen territories in various stages of recognition. The Alto Trombetas territories, upriver from Boa Vista, are among those still working through the process, with community associations such as Mae Domingas representing clusters of villages in the negotiation. Titling is not paperwork here. It determines who decides whether a logging permit is granted, where a mining road may run, and whether a family that has harvested the same Brazil nut grove for four generations gets to keep doing it.

Oriximina is the westernmost municipality in Para and the second largest by area in the state, which also makes it the fourth largest in Brazil. The Equator crosses it. The town itself sits on the Trombetas about 40 kilometers northwest of Obidos, at the narrowest point of the whole Amazon, and it has held municipal status since 1877. Almost everything beyond the riverfront is forest. Roads are few, the river is the highway, and distances that look modest on a map are measured in days rather than hours. The municipal boundary encloses more intact rainforest than most nations possess in total.

In 1979 the federal government created the Rio Trombetas Biological Reserve, just over a million hectares of strict protection, established in large part to defend the nesting beaches of the Arrau turtle, the giant of South American rivers, whose eggs had been harvested to the edge of collapse. The same stretch of river holds Porto Trombetas, a company town built around a bauxite operation big enough to need its own airport 70 kilometers from Oriximina proper. Aluminum ore and turtle beaches share a watershed, and the quilombola communities live between them, which is why so much of the region's politics turns on boundaries drawn on maps in Brasilia. The Saraca-Taquera National Forest, created in 1989, adds another 441,283 hectares of sustainable-use land to the same mosaic.

Most of the northern part of the municipality falls inside the Grao-Para Ecological Station, which at more than 4.2 million hectares is the largest fully protected tropical forest conservation unit on the planet; Oriximina holds close to 76 percent of it. Add the 3.1-million-hectare Trombetas State Forest, 88 percent of which is also here, and the picture becomes clear. This corner of Para anchors one of the largest continuous blocks of standing forest left anywhere, running north to the frontier with Guyana and Suriname. It survives partly because of decrees signed in distant capitals, and partly because the people living along the Trombetas made the case, community by community, that the forest was already somebody's home.