Early Christianity
According to Fritz Blanke in his book Urgeschichte des schweizerischen Christentums (Prehistory of Swiss Christianity), we have to thank Irenæus, Bishop of Lyon, for the first mention of Christianity in Switzerland. He said that around about ad 180 there were Christian «churches» in the territory of the Helvetii and the other Celtic peoples, namely the Allobroges in Geneva. Blanke writes that during the period ad 260-401 Christianity was first a permitted religion within the Roman Empire (ad 311), and then became the state religion (ad 380).
At this time, «Helvetia» was also part of the Roman Empire but historians assume, though, that the Christian faith was only able to become established in the Roman settlements; outside these areas – in the country – the «indigenous» religion managed to survive considerably longer. Archaeological evidence of the earliest churches in Switzerland can be found in Martigny (VS) and in Geneva. At the end of the fourth century, there is evidence of there being Christian churches in Kaiseraugst, Zurzach, Windisch, Basel, Avenches, Nyon and Yverdon. The fact that the names of Swiss bishops are reported in acts of council allows us to conclude that Church structures had also been established at an early stage in Switzerland.