Whose expedition first explained the scale of the Amazon River basin to the wider world?

Alexander von Humboldt explored parts of South America from 1799 to 1804 and became one of the first great scientific interpreters of the continent’s rivers, including the Amazon system. Although he did not trace the Amazon from source to mouth, his observations helped Europeans understand its enormous scale, biodiversity, and climate links. Humboldt’s writings influenced geography, ecology, and the study of river basins. The Amazon would later be mapped in much greater detail by 19th-century expeditions.