Scholars agree that transport by rivers and lakes greatly stimulated the development of trade in the Roman empire. Waterways, however, are as much man-made as roads are. They require investment, regulation and control. Without tow-paths, canals, locks, connecting roads, ports and warehouses rivers offer only a marginal contribution to trade. Yet, the contribution of rivers and lakes to Roman transport networks is usually treated in a matter of fact way. This project will study the institutional conditions governing navigation on rivers and lakes, and the recource requirements for and effects of Roman interventions. Our approach is inspired by complexity economics, which analyses economics systems as dynamic networks of autonomous agents. We combine a social network analysis and a spatial network analysis to study the institutions, agents and spatial structures in the Rhone/Saone river basin and in the river basins of Scheldt and Meuse. Both areas differed institutionally and ecologically, but were interconnected via the Rhine and were part of a larger transport network linking the Mediterranean to the North Sea area.