the Tertiary Hills of Lower Bavaria all the way into the Danube valley. Its mouth at the Danube some five kilometres away from Deggendorf is at above sea level. Thus the Isar descends some from its head to its mouth. Islands Most of the small islands and gravel banks keep changing shape and size due to the annual floods. Some of the islands within the bigger cities were built up during the 19th century and thus protected against the abrasive powers of the water. Among those are the Museumsinsel (on which the Deutsches Museum is located); formerly this island was called Kohleninsel (coal island), the Praterinsel (both located in Munich) and the Mühleninsel in Landshut. History 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. At a few places the Romans built wooden bridges across the Isara so they could cross the river with its strong currents more easily. One of these could have been along the Roman road from Salzburg to Augsburg south of contemporary Munich. Thus trade traffic could easily be controlled and income from tolls was frequent and regular. The medieval foundation of the cities of Munich and Landshut are directly connected with the building of bridges and the resulting conflicts concerning power and influence on the economy. Due to the continuing growth of the cities there was a constant demand for timber and lime, which resulted in an increase of commercial rafting. Beginning in the 17th century wares like Mediterranean fruit, spices, cotton and silk from the Venetian Market in Mittenwald were transported down the Isar and Danube all the way to Vienna and Budapest. During the 19th century when commercial rafting was at its peak, some 8,000 rafts arrived in Munich each year. Since the Middle Ages water mills were working at the banks of the Isar by hydro mechanical power. To ensure a more constant flow for the mills the water in Munich was led into small canals. The canals were also used to provide freshwater to the population of