Hidden away within the Monastery of St John, which was founded, as tradition would have it, by Charlemagne, this church includes a triple apse in a cul-de-four. The nave was turned into a Gothic aisle in the 15C. The frescoes inside constitute the most important collection of murals in the Confederation. Some are on show in the Zurich National Museum. The oldest, partly covered, date back to the 9C.