By the 15th Century, Bern had expanded and become a major city-state north of the Alps. To celebrate their growing power and wealth, plans were made to build a new and larger church. On 11 March 1421 construction began on the cathedral under the direction of the Strasbourg master builder , who had already built three other cathedrals. During construction, services were held in the old chapel while the new cathedral was built up around it. During the 1440s the unvaulted choir was used for services after a simple roof was built and stained glass windows were installed. After the Old Zürich War 1440–1446 the nave of the old chapel was removed and work began on the nave and west end, under the chief masons Stefan Hurder and then Niklaus Birenvogt.