A new type of evidence exists now to document the history of infectious diseases in the past. But this evidence consists of millions of molecular fragments that have to be retrieved and analyzed by palaeobiologists, not historians. How do historians–who are accustomed to working with written documents–learn to assess a new kind of evidence? This essay makes an argument for the value of interdisciplinary dialogue, which can open up new questions and new lines of research even for a pandemic that occurred 1500 years ago: the Justinianic Plague (6th-8th century). Discussing the scope, impact, and causes of the JP is worthwhile for any number of reasons, but it has a particular value in allowing us to talk about how and why the field of genetics is playing a unique role in new approaches to the history of pandemic disease — and why it is broadening the question well beyond the boundaries of the Roman Empire as Gibbon envisioned it. This copy includes citations to all the works linked in the original blog.