 at the University of Bern in Switzerland with works about the social history of the Christians in the city of Rome in the first two centuries and about the concept of ecclesiastical unity in the Pauline letters.As assistant professor ("Wissenschaftlicher Assistent"), he taught at the University of Bern from 1981 on, until, in 1986, he was called to a chair of New Testament Studies at Union Theological Seminary in Virginia, USA.In 1992, he took the chair of History and Archaeology of Early Christianity and Its Environment at the University of Kiel in Germany, where he also served as dean of the school of theology.