The first church on the cathedral site was built in the first half of the 5th century. The Romanesque crypt was probably built under Bishop Tello (758-73). It contains remarkable paintings by Albrecht Dürer and Hans Holbein. The current building was built between 1154 and 1270. In 1272 it was dedicated to Saint Mary of the Assumption. The round arch window along the center axis is the largest medieval window in Graubünden. The late-Gothic high altar was completed in 1492 by Jakob Russ.