The smallest river would become a barrier, only to be crossed by boat, or a place where the water is shallow enough to wade through. Railways and motorways would be impossible dreams. Journeys that are just a few miles as the crow flies would have to follow a roundabout route to avoid difficult streams and rives. And if there were heavy loads to be carried, the journey would take even longer. Without bridges, all communication would slow down and without swift reliable communication civilization would not be able to develop beyond the stage of small and mainly isolated settlements.
Bridges help human being and other earthly creatures a lot.