Analyzing the history of fish populations in the Neva and Viennese Danube, the Russian-Austrian research group discovered numerous links between the great cities and their great rivers, including the fish populations. This introduction to the virtual exhibition “‘Commanding, Sovereign Stream’: The Neva and the Viennese Danube in the History of Imperial Metropolitan Centers” explains how the exhibition visualizes these links and reveal some hidden (or at least not immediately evident) sides of urban life.