Switzerland is an ideal banking country in geopolitical terms. It borders with three major economies, but is also an easily defendable mountain fortress. It has remained largely undisturbed because it would simply cost too much to invade.
That's why, for hundreds of years, it has been a banking mecca. Europe has been wracked by war for centuries, during which banking houses are periodically plundered by invading armies. But Switzerland with its defensive advantages and long history of neutrality rises above the noise. If you're a rich European, the safest place to park your money in the past 1000 years has been Switzerland.