The earliest New Testament manuscripts are notoriously difficult to date, with informed guesses sometimes differing by more than a century. But even the most optimistic scholars would not claim to know of a fragment of any New Testament book that comes from the first century and could, therefore, have been handwritten by its assumed author (Matthew, Paul, etc.) or by his contemporary. This applies also to the recently debunked “first-century Mark” (Papyrus Oxyrhynchus 5345).
Establishing precise dates of secular documents, on the other hand, is often possible, because these everyday writings may contain a date or a historical clue allowing for an informed guess. To identify authors of such documents as Christian, however, can be tricky, because letters, inventories, or contracts do not typically signal the religious identity of their writers. But there are exceptions.
A Swiss scholar was recently able to pinpoint the oldest Christian letter from circumstantial evidence. Professor Sabine Huebner’s analysis of Papyrus Basel 2.43 reveals that it belongs to the famous Heroninus Archive from Theadelphia in the Fayum of Egypt. The events and people mentioned in the letter are known from other, reliably dated documents and position this one to the early 230s—about a half century prior to any other securely dated evidence. The Christian identity of the author is then given away by a distinctly Christian phrase and the way it is abbreviated.