During the middle of the eurozone crisis, investors piled into assets they considered safe. The price of gold, for example, soared. The precious metal was thought likely to maintain its value even amid economic turmoil. 

The same logic applied to Swiss assets. Money piled into the country. The Swiss central bank decided to implement a minimum exchange rate - capping the value of the franc at just over €0.83 - in order to keep things under control and ensure the country's exporters were not hurt by the franc getting too strong. 

On Thursday, the SNB said: "The minimum exchange rate was introduced during a period of exceptional overvaluation of the Swiss franc and an extremely high level of uncertainty on the financial markets. This exceptional and temporary measure protected the Swiss economy from serious harm."

While the euro crisis hasn't exactly gone away, new themes in currency markets have emerged. The dollar has gained strength, pulling away from the euro amid signs that the Federal Reserve may be ready to increase its interest rates. 

Simultaneously, the outlook for the eurozone has deteriorated. Analysts now expect that this can only be address if the European Central Bank engages in outright quantitative easing. This could further depress the value of the euro. The SNB said that the divergence between the dollar and euro is "a trend that is likely to become even more pronounced". 

The SNB thinks the franc is no longer as overvalued as it was in 2011, so the cap can go.