One castle (schloss) after another lined the hillsides. As it turns out, the castles were originally owned by nobility and high ranking Catholic church figures (archbishops). Most of the castle owners were granted the right to collect tolls from ships traveling on the Rhine. This practice existed for 1,000 years from 800 to 1800 AD and it kept the collectors very wealthy. Around 1250 AD, some people decided it would be a good idea to collect tolls without the sanction of the church. Those people were referred to as "robber barons" and were eventually put out of business and their castles destroyed.
Typical Rhine River city.