The park's position is not accidental; it is a survey line that turned into a place. In 1627 the Portuguese Crown granted Belém's city council a patrimonial league of 4,110 hectares, running inland from the banks of the Pará and Guamá rivers, in order to push settlement away from the waterfront and into the interior. The outer edge of that grant became known as the Marco da Légua - the league marker - and a neighborhood grew around it. Two years earlier the Portuguese had set up a customs warehouse at the harbor to weigh and tax imported European goods, the beginning of what would become the Ver-o-Peso market. Between the tax house at the water and the marker a league inland, the colonial shape of Belém was drawn. The park sits precisely on that boundary.

José Coelho da Gama e Abreu, the Baron of Marajó and president of the province of Grão-Pará, had seen the Bois de Boulogne in Paris and wanted one for Belém. The wood at Marco da Légua had been set aside by provincial law in September 1870; in August 1883, under Emperor Pedro II, it opened as a municipal park. This was the Belle Époque of the Amazon, when rubber money made ambitions of that scale seem reasonable, and a public forest on the road out of town read as a declaration that Belém was a modern capital. In 1903 the intendant Antônio Lemos reopened the grounds with the picturesque apparatus of the period - waterfalls, artificial lakes, grottos. The paths were laid so that citizens could stroll through their own rainforest in city clothes.

Much of that nineteenth-century staging survives. The monumental iron gate still frames the entrance. Inside stand a monument to the city's intendants, a Chinese kiosk, a cave built of soapstone, and the artificial lakes, along with a nineteenth-century house restored and moved onto the grounds in 1985. The most telling piece is a statue of Mapinguari and Curupira, guardian figures from Amazonian folklore who are said to protect the forest and punish those who take more from it than they need. Setting them at the heart of a park designed in imitation of Paris says something about how Belém has always negotiated between the two worlds it belongs to.

The park holds more than 300 species of plant and 58 species of animal, roughly 435 individual animals in total, and the arrangement is unusual: some are captive, some semi-captive, and some simply live there. Free-ranging mammals, birds, amphibians and reptiles share the forest with animals in enclosures and fish in tanks, and a bird nursery supports the wildlife management and environmental education programs. Parrots, parakeets, maitacas, jandaias, maracanãs and scarlet macaws move through the native canopy, along with an endangered large blue macaw. Around 20,000 people come through the gates each month. In 2002 the site was provisionally registered as the Amazon Botanical Garden, and in 2008 it was formally elevated to botanical garden status, joining the Botanic Gardens Conservation International network.

A fragment this size cannot preserve an ecosystem; the Amazon does not work at that scale. What it preserves instead is a reference - a standing sample of what the ground under Belém looked like before the ground under Belém was a city, close enough to downtown that a schoolchild can visit it on a weekday morning. The remaining six percent of the vegetation is exotic, the residue of a century of gardeners. The other ninety-four percent was never planted by anyone.