Even though supported by massive pillars , an earthquake in 1356 destroyed five towers , the choir and various vaults . Johannes von Gmünd , who was also the architect of Freiburg Minster , rebuilt the damaged cathedral and in 1363 the main altar was consecrated . In 1421 Ulrich von Ensingen , who constructed the towers of the minsters in Ulm and Strasbourg , began the extension of the northern tower ( '' Georgsturm '' ) . This phase ended in 1429 . The southern tower ( Martinsturm ) was completed by Hans von Nussdorf on 23 July 1500 . This date marks the official architectural completion of the minster . In the 15th century the major and the minor cloisters were added . The minster served as a bishop ’s see until 1529 during the Reformation . Today 's congregation forms part of the Evangelical-Reformed Church of the Canton Basel-Stadt . In the 19th century two major restorations took place . From 1852 until 1857 the rood screen was moved and the crypt on the western side was closed . In the 20th century the main aim of renovations has been to emphasize the late Romanesque architecture and to reverse some modifications made in the 1850s . Additionally , the floor was returned to its original level in 1975 and the crypt reopened . A workshop dedicated to taking care of the increasingly deteriorating sandstone exterior was set up in 1985
earthquake in 1356
1356 Basel earthquake
Basel Minster