Brazil–Peru border

The 1851 line

In 1851, when Peru seemed to control the land between the Amazon and the Apaporis–Caquetá confluence, Brazil and Peru agreed a boundary running from the Brazilian settlement of Tabatinga to the mouth of the Apaporis. Colombia protested. When Peru gave up that area to Colombia in 1922, the old Brazil–Peru line north of the Amazon became part of Brazil’s border with Colombia instead.^[1]

South of the Amazon, the 1851 treaty’s line along the Yavarí had already been demarcated by 1909, from the river’s source north.^[2]

The 1909 treaty

On 8 September 1909 Peru’s envoy Hernán Velarde and Brazil’s foreign minister, the Baron of Rio Branco, signed a treaty fixing the line south and east of the Yavarí’s source, through the upper basins of the Juruá, Purús and Acre. A joint commission was to mark it within a year of ratification; disagreements that the governments could not settle would go to three members of the French Academy of Sciences or the Royal Geographical Society.^[2]

A 1913 protocol set the commission to work river by river: surveying the Shambuyaco and Santa Rosa, tributaries of the Purús, whose deepest channel forms the border between them; tracing the divide between the Envira and the Curanja and on to the source of the Breu; and fixing the mouth of the Yaverija on the upper Acre. The treaty also promised free navigation on all the border rivers, with Peruvian ships free to reach the Atlantic down the Amazon.^[2]

“Los buques peruanos destinados a la navegación de esos ríos comunicarán libremente con el Océano por el Amazonas.”^[2]