In the 1970s, a graduate student doing his thesis on St. Patrick was told that another student had already chosen the same topic. Forced to change topics in the middle of his studies, he did his dissertation on Historia Brittonum. That decision turned out well for historical studies. Dumville provided a number of valuable insights on the manuscript and its author, eventually providing a complete history. As an established scholar, he later returned to his original interest and clearly laid out all the arguments about Patrick’s chronology. He has also done work on a number of other manuscripts relating to the period, always providing precise histories with his exacting methods. It is for this reason that he was made a Full Professor at Cambridge.
In addition to his work with manuscripts, his reputation has allowed him to try his hand at an overall study of the period on several occasions. Here his need for exactness has left him unable to see beyond the limitations of the relevant sources. His conclusions have invariably been that our knowledge of the period is a complete void and must remain so because there are no sources that are up to his rigorous standards. It is unfortunate that his weaknesses as a scholar, his reputation, and his need to broaden his horizons have combined to put such a formidable barrier to post-Roman studies.