To judge from the literature on Roman engineering, there was a time when the history of bridge building was a prominent theme closely associated with a parallel and equally well-developed interest in Roman roads. Recently, as a result of a variety of new approaches to archaeological, technical and social themes, the emphasis has moved to aspects of hydraulic engineering and, in particular, problems of water power and water supply. Of course, fashions in engineering history, Roman or later, are bound to change from time to time. That is understandable and nothing new. On the other hand, any overall view of Roman civil engineering needs to integrate the various approaches, especially in so far as they affect one another. Bridge building, after all, is bridge building, whether the structures are for roads or aqueducts and, in this lecture, both functions will be considered.