The lower Amur River basin was annexed by Russia in the mid-nineteenth century following several years of unauthorized exploration by naval officer Gennadii Nevel'skoi. Scholars recognize multiple factors—geopolitical, economic, and nationalist—that prompted Russia's interest in the region. This article adds to this list the budding science of geography, and in particular, the influence of German geographer Karl Ritter. To Ritter, a nation's true borders were set by nature, not by man. His ideas are reflected in both the words and actions of Nevel'skoi regarding the lower Amur basin. The explorer described the territory not as foreign or other, but as naturally, historically, and rightfully Russian land. The river, to him, was a highway, facilitating transport through Siberia. In time, even the tsar was convinced. Ritter's ideas extended far beyond intellectual circles in Russia, serving to at once guide and justify Russia's eastward expansion.