 In 1999, he accepted a call to the University of Heidelberg.His works focus on the social history of early Christianity (groundbreaking studies on, for example, early Christianity in Rome in the 1st/2nd centuries, and on Paul's correspondence with Philemon; his work also contributed decisively to the paradigm shift toward a more contextual reading of the Letter to the Romans); on the Hellenistic background of early Christianity; on Pauline studies (including rhetorical studies); on early Christian archaeology and epigraphy; as well as on methodological and hermeneutical questions.He pioneered applying constructivist categories to New Testament exegesis and hermeneutics.