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.