In the last decades of the 19th century, the Amazon economy ran on latex. Rubber trees grew wild in the Juruá basin, and anyone who could tap them stood to make fortunes - or at least wages - in an industry whose global demand was exploding with the bicycle and then the automobile. Peasants fleeing drought in Brazil's Northeast - from the states of Ceará, Rio Grande do Norte, and Paraíba - came west to the rubber frontier. They were brought in part by a man named Felipe Manoel da Cunha, a wealthy seringalista who owned the Eiru plantation. The men arrived without women. They married into the Kulinaã, a local indigenous group, creating a population shaped by that particular mixing. The Kulinaã who accepted the incomers became known as Kulinas; those who refused took the name Kanamari. The two names still carry the memory of that choice.

During the First World War, a second wave arrived. People fleeing the fighting in Europe came looking for any kind of new life and found the Juruá. Some were Turkish, some Portuguese, others from further afield. The rubber boom was still paying, barely, and the jungle absorbed them. When rubber prices finally collapsed for good, many families migrated away again, mostly toward Manaus. Others stayed, scraping livelihoods from smaller-scale latex extraction and subsistence agriculture. The result was a population unusual even by Amazonian standards: Northeastern Brazilian, indigenous, European, blended over a century. The local culture carries traces of all of it - food, language, music, customs whose origins have since become impossible to fully separate.

Eirunepé has been called several things. In the 1890s, the settlement around the Eiru plantation went by the name San Felipe do Rio Juruá. A state law in 1892 formally created the municipality under that name, but the law was not actually implemented. Another law in 1894 created a judicial seat. Boundary revisions in 1896 moved things around. After the Brazilian National Revolution of 1930, the town was renamed João Pessoa. In 1935, it was elevated to city. Finally, on December 31, 1943, State Decree Law No. 1186 settled the name as Eirunepé - a transliteration of Eiru, the original plantation name. In 1955, part of the territory was split off to form two new districts called Envira and Ipixuna. What looks like administrative tedium is really the slow, stubborn process of a place figuring out what to call itself.

The climate sits under the Köppen Af classification - equatorial, constantly humid, with average temperatures around 26 degrees Celsius. Annual rainfall runs about 2,300 millimeters. Most of the year feels predictable: hot, wet, green, loud with insects. But then, from June to August, the friagem arrives. Polar air masses pushing north from the Antarctic reach all the way into the western Amazon, and temperatures can drop to 15 degrees Celsius or lower. On June 1, 1988, Eirunepé recorded 8.5 degrees Celsius - a number that would be unremarkable in many places but in a jungle town on the equator feels like an alarm. The record high hit 39.8 degrees Celsius in October 2015. The daily heat does not vary much; the seasons arrive instead as rain or as brief, disorienting cold.

Eirunepé sits inside the Rio Gregório Extractive Reserve, which covers 427,004 hectares and protects 41.22% of the municipality's land. The reserve exists to let traditional rubber tappers and river communities continue their way of life while formally protecting the forest against encroachment. There is also a proposal - revived periodically in Brazilian politics - to carve a new state called Juruá out of southwestern Amazonas. If that ever happened, Eirunepé has been named as a candidate to become its capital. The prospect remains theoretical. For now, the town remains a fourth-largest city in the Southwest region of Amazonas state, served by Amaury Feitosa Tomaz Airport, connected to the outside world by river, a twice-weekly flight, and the long memory of Felipe Manoel da Cunha's plantation along the bend.