Almost everything around here is floodplain. The Amazon at this latitude is a world of várzea and shallow lake and low green horizon, which is what makes the Monte Alegre uplands so startling: abrupt sandstone ranges, the Paytuna and the Ererê, standing out of it with cliffs, cave mouths and sightlines that run for tens of kilometres. The park sits entirely inside the larger Paytuna Environmental Protection Area. Its slopes carry a dry, scrubby vegetation quite unlike the rainforest most people expect of Pará, and the sulphur-breasted parakeet, Aratinga maculata, is endemic to this region and nowhere else. From the Pedra do Mirante, a rock that can be climbed, the view opens through a full three hundred and sixty degrees over hills, forest and the great brown river below.

The Gruta da Pedra Pintada - Painted Rock Cave - opens on the eastern flank of the Paytuna range, 120 metres above sea level and 89 metres deep, a sequence of corridors and halls. Between 1990 and 1992 the American archaeologist Anna Curtenius Roosevelt excavated it, and what came out of the floor unsettled a comfortable assumption. The Amazon, the textbooks had said, was a marginal environment settled late. The deposits said otherwise: some thirty thousand stone artefacts, including triangular stemmed points quite unlike the fluted Clovis points of North America, lying alongside charred Brazil nuts, palm seeds, fish bones, shellfish, birds, reptiles and amphibians. These were not big-game hunters following mammoths. They were people who knew a tropical forest intimately and ate very well from it. Fifty-six radiocarbon dates on carbonised plant remains and thirteen luminescence dates on stone and sediment placed the earliest occupation at roughly 11,200 to 10,000 years ago.

Roosevelt published in Science in 1996, and the challenge arrived quickly. C. Vance Haynes of the University of Arizona, a famously conservative reader of Paleoindian chronology, argued that a stricter statistical treatment of the same dates would pull the occupation no earlier than about 10,500 years ago - late enough for the people of Pedra Pintada to be descendants of Clovis rather than their contemporaries. Roosevelt's reply was pointed: apply that standard to Clovis itself, she wrote, and Clovis becomes too recent to be anybody's ancestor. Nobody accused anybody of sloppiness. The dispute was about how tightly a date can be tied to the layer it came from, and it has never been fully resolved. The paintings are harder still, since pigment carries no radiocarbon date of its own; Roosevelt worked from paint droplets and pigment lumps found in the excavated floors, and Brazilian researchers have since revisited the chronology of the art with new data. What is not in dispute is that people were living in this cave at the end of the Pleistocene.

Pedra Pintada draws the tourists, but it is one of many. The Gruta do Pilão holds paintings of its own and ranks among the oldest archaeological sites in the Amazon. The Gruta Itatupaoca, also called the Gruta da Capela, runs 56 metres into the southern slope of the Ererê range, its 9.5-metre entrance split down the middle by a rock column. The Gruta do Miritiepé goes 87 metres into the northwest flank of the Paytuna, a well-lit gallery opening into a chamber named for the leaves that carpet its floor. The Gruta do Labirinto lives up to its name at more than 90 metres. And there is more to find: in November 2012 researchers from the Museu Paraense Emílio Goeldi reported nineteen previously unrecorded sites in the lower part of the park, with rock paintings and ceramics.

Monte Alegre was the first conservation unit in Pará created with the participation of the people who live around it, an approach that grew out of state research institute studies at the end of the 1980s. The park was established by law in November 2001 at 5,800 hectares; a consultative council was named in 2009, a management plan approved in 2010, and in January 2013 a boundary correction transferred 2,122 hectares to the surrounding protection area, leaving the present 3,678. Then came the harder question of who benefits. In April 2013 the Peabiru Institute selected five initiatives to help local women and young people supply guiding and hospitality services, under a project training Monte Alegre ecotourism agents. Rock art that has lasted eleven thousand years can survive visitors. Whether it earns anything for its neighbours is a decision made in the present.