The choir, raised above a crypt, consists of a short, straight bay preceding a polygonal apse with an ambulatory. The choir arcades, which increase in height towards the apex, rest on clustered piers; the gallery, which was reconstructed after the earthquake, has a single opening screened by tracery bars, which are extensions of the clerestory mullions.

Bâle is the French name for Basel. Originally a Catholic cathedral it is today a reformed Protestant church (munster or minster). Dedicated to the Virgin, it is essentially Late Romanesque or Early Gothic, standing on the foundations of successive Ottonian and Salian buildings, which largely governed its dimensions. It was probably started before a fire of 1185 and it was completed shortly after 1200. The towers, main vault and the upper storeys of the choir, which collapsed in the earthquake of 1356, were mainly rebuilt by Johann von Gmünd. The two-tower façade was altered during the 15th century: the northern Georgsturm was extended (1421-1428) to the designs of Ulrich von Ensingen and the southern Martinsturm was extended between 1488 and 1500. Erasmus and Bernoulli are buried in the church.