Two Franciscan friars, under threats from nearby natives in 1637, abandon their mission on the Amazon River and, with six soldiers, paddle a canoe up the entire length of the river to the principal Portuguese settlement of Fort Presépio in present Belèm.

Their arrival leads the Portuguese to wonder how far east the Spaniards have settled the Amazon.

Although Spain and Portugal are both under the rule of Philip IV of Spain (Philip III of Portugal), trading rivalry is nevertheless intense and there is a strong movement towards the restoration of the Portuguese independence.

Consequently, the governor of Maranhão, Jacome Raimundo de Noronha, loses no time in commissioning an expedition under the command of Captain Pedro de Teixeira, who already has considerable experience exploring the Amazon and the Xingu River leading expeditions to expel English and Dutch traders and settlers.

One of the Franciscan friars, Andres de Toledo, is dispatched to Lisbon to report his expedition to the Portuguese authorities.

Teixeira thus becomes the first European to travel up the Amazon River, reaching Quito by way of the Napo River.

The Portuguese expedition is a large one, consisting of forty-seven canoes powered by twelve hundred natives and Negroes to transport 70 fully armed Portuguese soldiers and their cargo of food, weapons, ammunition and barter goods.

Feeding so many over a journey of several months is a formidable task, demanding the most of the explorers' hunting, fishing and food gathering skills, and often requiring barter with local tribes.

The journey upstream against a strong current is arduous, and advance parties are regularly sent out to reconnoiter the way ahead in order to identify the correct fork in the river to take.

Teixeira also has difficulty persuading the natives to stay with the expedition as it gets farther from their homes.

After eight months, the Portuguese reach the first Spanish settlement on the Rio Quijos.

At this stage, Teixeira divides the expedition, sending eight canoes ahead whilst the remainder are to stay at the settlement for the return journey.

The Rio Quijos is eventually abandoned when the current grows too strong, and the rest of the journey is completed on foot.