Brazil–Colombia border
The border between Brazil and Colombia is 1,644.2 km (1,021.7 mi) long. The boundary was delimited in two treaties: the Vásquez Cobo-Martins treaty of 1907, establishing the line from the Rio Negro northwestward along the Amazon River-Orinoco watershed divide, "then generally southward along various river courses and straight-line segments to the mouth of the Apaporis River", and the Tratado de Límites y Navegación Fluvial of 1928, delimiting the Apaporis-Amazon segment of the boundary as a "geodesic line identical to its Brazilian-Peruvian antecedent after Colombia gained undisputed sovereignty over the area".