Regensburg was Medieval South Germany's most important centre for architecture

Because of its economical and political significance in the early and high Middle Ages, Regensburg became a key location for town planning north of the Alps. This is true of both religious and secular architectural constructions, some of the most outstanding achievements of that era. Traces of human presence in Regensburg have been found dating all the way from the early Stone Age and from every era that followed. Archaeological finds tell of early trade relations all the way to the Black Sea. In the early Middle Ages, Regensburg's architecture as an ambitious trade centre had a permanent effect on town planning north of the Alps. This is true of the many exemplary construction achievements, religious and secular, clustered around Regensburg and far into its rural district, and also of the city's development as a whole: between 917 and 920, Duke Arnulf of Bavaria built a wall around the entire western city including the large grounds of St. Emmeram's abbey.

Pictures:

Stone Bridge, Town Hall, Runtinger House, St. Peter's Cathedral,
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No comparable wall was built in any other European city until after the millennium. It is the first documented post-classical city expansion north of the Alps. The large Romanesque and Gothic church buildings and monastery complexes - St. Emmeram, the Old Chapel, the Lower Minster, St. Jacob's and the Cathedral - are exceptional artistic accomplishments for their time. The churches of the mendicant religious orders of the Dominicans and the Conventual Franciscans are very early architectural examples of changing religious beliefs in the late Middle Ages.
The late Gothic town hall complex shows an excellent construction of all the functional parts of a medieval town hall. The Stone Bridge, built between 1135 and 1146, is an absolutely unique medieval feat of engineering, and for a long time it was the only walled Danube crossing between Ulm and Vienna.