I hope this question isn't too specific. I was looking at some Brazilian maps in Wikipedia and I noticed that sometime between 1822 and 1889, the border between the Mato Grosso and Grão-Pará (later just Pará) provinces changed from a very squiggly line into a completely straight one. I tried doing some searching on the matter but couldn't find anything, so I decided to ask about it here.
When exactly did the change occur? Did they do it via some treaty? If so, what treaty was it? And lastly, what was the reason behind the change? Were the older borders causing conflict or something in the region?
When exactly did the change occur?
The present-day states of Mato Grosso, Pará and Amazonas were still under exploration and early settlement in the 18th century. By royal decree, the captaincies of Goiás and Mato Grosso were created in 1744 and 1748, respectively. Pará, whose first settlement dates from 1616, was made a captaincy in 1772-74.
Despite occasional visitations from bandeirantes, what is now the border between the North and Central-West regions were an unsettled and largely unknown jungle. In 1771 the governors of Mato Grosso and Goiás, for example, had to agree to a provisional border between their captaincies, since the Overseas Council set no boundaries in there
Maps from the 19th century show sharply different borders. Some illustrate a straight line over the 9th parallel south or between it and the 10th; others show interstate lines following the confuse, doubtful courses of Amazonian rivers. "The desert spares all borders; indeed, it suppresses them".
Evolution of northern interstate boundaries in maps
In the late 19th century, however, the Northern desert saw a growing influx of immigrants. The question of interstate boundaries could no longer be ignored. It was also a time of great scientific expeditions and Brazil was making the effort to link together its vast territory. In 1890 Cândido Rondon made his first expedition to Mato Grosso in order to establish telegraph lines in the isolated state. In 1895 the government of Pará supported a reconnaissance mission in its southern rivers led by French geographer Henri Coudreau.
In 1895 the president of Mato Grosso fixed the borders at the Tapajós and São Manuel rivers. In 1898 the president of Pará was reached out for an agreement on the subject. After a period of negotiations, the two states recognized in 1900 the following interstate border, implemented by presidential decree in 1919:
"§ 1º The territory north of the S. Manoel river to the Sete Quedas falls, and from the Sete Quedas falls to the western bank of the Araguaia river, in the fixed location, will belong to the state of Pará, and the lands to the south will belong to the state of Mato Grosso".
The northern boundaries in 1922
Wikipedia's 1889 map is wrong, as usual.
The first attempt to set a boundary between Mato Grosso and Amazonas, then known as the captaincy of Rio Negro, was made in 1758. The governor-general of Brazil Mendonça Furtado sent a reconnaissance mission to the north in order to delimitate the two provinces. The expedition set the Madeira, the Jamari and the Ji-Paraná rivers as the inter-provincial boundary. No further questions emerged until the late 19th century.
Rubber extraction had become a growing industry along the Madeira river. A dispute between Mato Grosso and Amazonas arose when Mato Grosso officials attempted to tax the enterprise in the 1890s. Amazonas then attempted to sue Mato Grosso in 1896. in 1899 the Supreme Court ruled in favor of Mato Grosso and set the boundary at the 8th 48' parallel south.
The boundary between Mato Grosso and Pará remained a contentious issue, however. There was a confusion regarding two homonymous localities called "Salto das Sete Quedas" and "Cachoeira das Sete Quedas. Cachoeira and salto are different types of waterfalls. In 1988 the Diário de Cuiabá, a mato-grossense newspaper, claimed that part of Pará's southern territory belonged to Mato Grosso, and that the official map drawn by the Clube de Engenharia in 1922 was defective due to the aforementioned issue of waterfalls.
In 2004 Mato Grosso sued Pará. The dispute was solved only two years ago (2020) by the Supreme Court. The rapporteur minister and the court ruled in favor of Pará:
"The landform which was agreed upon as the limit point between the state of Pará and Mato Grosso, in the Convention of 7 November 1900, approved by the presidential decree no. 3.679/1919, is the southernmost one, of coordinates 9º 22’S e 56º 40’W Gr, named, until 1952, as "Salto das Sete Quedas", and from that year on, as "Cachoeira das Sete Quedas" in contemporary maps and atlases".
Present-day map with the territory formerly claimed by Mato Grosso
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