the underlying explanation of all the other answers is: "its on the Rhine and quite north". The Rhine is historically the most important river of the area, so b

the underlying explanation of all the other answers is: "its on the Rhine and quite north". The Rhine is historically the most important river of the area, so big cities and populations sprang on it. And, strangely, the Rhine is/was an important connexion to the UK, hence the importance of Frankfurt even on a quite large scale. Today it still makes sense to go there because Germany is the wealthiest country around, and from there you can serve the entire Paris-Brussels-Amsterdam-Frankfurt area, which includes a lot of people: http://kids.britannica.com/comptons/art-143547/Population-density-of-Europe-and-the-Caucasus-region http://kids.britannica.com/comptons/art-143547/Population-de... edit: before I get punched by an autist, Frankfurt not ON the Rhine, but it has an incredibly quick access to the Rhine without being subject to its floods.