Hamburg is a large city of 1.8 million inhabitants and a major harbour in northern Germany. It lies on the river Elbe at the confluence with the Alster and Bille rivers. Its port is third-largest in Europe and the ninth largest in the world. The city has a vibrant economy, being a media and industrial center and a major transportation hub. Hamburg has an important assembly plant in Finkenwerder for Airbus, the aircraft manufacturer. It dates back to 808 AD, when a fortress was built on rocky terrain between the rivers Alster and Elbe as a defence against Slavic incursions. Its major development started in 1189 when Emperor Frederick I ("Barbarossa") granted Hamburg the status of an Imperial Free City and an exemption from customs duties.