At the other end of the Empire, in Germania, the navy played an important role in the supply and transport of the legions. In 15 BC an independent fleet was installed at the Lake Constance. Later, the generals Drusus and Tiberius used the Navy extensively, when they tried to extend the Roman frontier to the Elbe. In 12 BC Drusus ordered the construction of a fleet of 1,000 ships and sailed them along the Rhine into the North Sea. The Frisii and Chauci had nothing to oppose the superior numbers, tactics and technology of the Romans. When these entered the river mouths of Weser and Ems, the local tribes had to surrender.