The Lower Danube—the stretch of Europe’s second longest river between the Romanian-Serbian border and the confluence to the Black Sea—was effectively transformed during the late eighteenth and nineteenth centuries. In describing this lengthy undertaking, Luminita Gatejel proposes that remaking two key stretches—the Iron Gates and the delta—not only physically altered the river but also redefined it in a legal and political sense. Since the late eighteenth century, military conflicts and peace treaties changed the nature of sovereignty over the area, as the expansionist tendencies of the Habsburg and British Empires encountered rival Ottoman and Russian imperial plans. The inconvenience that the river’s physical shape obstructed free navigation and the growth of commercial traffic, was an increasing concern to all parties. This book shows that alongside imperial aspirations, transnational actors like engineers, commissioners and entrepreneurs were the driving force behind the river regulation. In this highly original, deeply researched, and carefully crafted study, Gatejel explores the formation of international cooperation, the emergence of technical expertise and the emergence of engineering as a profession. This constellation turned the Lower Danube into a laboratory for experimenting with new forms of international cooperation, economic integration, and nature transformation.