It is quite likely that the Isar was used as a trade route, even in prehistoric times, to transport wares from the Alps and even Italy towards the Danube with rafts. An existing trade road from the Inn valley across Seefelder Pass into the northern foothills of the alps was built up and called Via Raetia by the Romans. The town of Mittenwald thus became an important trade post in the Werdenfelser Land.