Chronology’s Forgotten Medieval Pioneers

by guest contributor Philipp Nothaft

According to a metaphor once popular among early modern scholars, chronology is one of the “two eyes of history” (the other being geography), which is an apt shorthand for expressing its tremendous utility in imposing order on the past and thereby facilitating its interpretation. Yet in spite of the undiminished importance chronology possesses for the study and teaching of history, latter-day historians tend to lose relatively little sleep over the accuracy of the years and dates they insert into their works. Assyriologists may continue to argue among themselves about variant Bronze Age chronologies, but for that happy majority focused on the development of civilization since the dawn of the first millennium BCE, errors in historical dating appear to be a local possibility rather than a global one. We may be wrong in attributing a Greek astrological papyrus or the foundation of a Roman military fortress to, say, the late second rather than the early third century of the common era, but even then we remain secure in the knowledge that the centuries themselves retain their accustomed place, containing as they do a fixed and familiar inventory of historical events. On the whole, it looks like the timeline is under our control.

Like so many amenities of modern life, this feeling of security is the hard-won result of a long process of trial and error, one that can be shown to have started a good deal earlier than commonly assumed. For the thirteenth-century Dominican philosopher Giles of Lessines, who turned to historical chronology in a pioneering Summa de temporibus (ca. 1260–64), the intervals of years between the major events of biblical and profane history were still a bewildering patchwork of individual puzzles, not all of which allowed for an easy solution. Problems were posed above all by the Old Testament, which in spite of its status as a divinely inspired, and hence exceptionally reliable, record of history since the world’s creation confronted Christian historians with a range of pitfalls. Even those who felt equipped to smooth out some of the contradictions encountered in the Bible’s chronological record still had to admit the existence of two discrepant versions: the Hebrew Masoretic text, represented to Latin Christians by St Jerome’s Vulgate translation, and the Greek Septuagint, which differed from the former in several numerical details. On Friar Giles’s count, the Greek translation added a total of 1374 to the Vulgate’s tally of years between Creation and Christ, which effectively double the nine different chronological readings he had been able to extract from the “Hebrew truth,” leaving him with a range of possibilities between 3967 and 5541 years. The margin of plausible intervals was mystifying and threatened to expose the scriptural exegete to the same sort of uncertainty that was encountered in profane chronicles and works of history, where scribal corruption, but also mendacity and ignorance on the part of authors, could mean that dates, years, or even centuries suddenly vanished or were retroactively inserted into the historical record.

In spite of such discouraging signals, Giles of Lessines believed that he had identified a class of sources that was worthy of his unreserved trust: works of astronomy, which linked observed phenomena such as eclipses of the sun and moon to particular dates in history, usually identified according to years of the reigns of ancient kings and emperors. Since these observations provided the raw material for astronomical theories, which in turn underpinned computational algorithms and the tables based on them, it was possible to assess their trustworthiness long after the event. Astronomical books, Giles wrote, “depend on years in the past being noted down with utmost certainty—otherwise the rules and principles they contain would not be dependable for the future” (Summa de temporibus, bk. 2, pt. 3, ch. 2). The predictive success of mathematical astronomy hence guaranteed the accuracy of the underlying chronological data, and vice versa. Friar Giles’s pièce de résistance in exploiting this insight were three lunar eclipses the Alexandrian astronomer Ptolemy had observed during the reign of the Roman emperor Hadrian: more specifically in years 133, 134, and 136 CE. As a seasoned astronomical calculator, Giles was able to use the specific criteria of these eclipses (their time, magnitude, and location) to establish the interval between Ptolemy’s observations and the present. The exercise gave him an entering wedge into the chronology of the Roman Empire, which, among other benefits, made it possible to confirm—against certain medieval critics—that the Church’s practice of calculating the years of Christ’s birth from 1 CE rested on a sound historical basis.

Giles of Lessines was far from the only medieval author to experiment with astronomical techniques in an effort to put chronology on a sure footing. A prominent case is the English Franciscan friar Roger Bacon (ca. 1214–1292?), who had read Giles’s Summa de temporibus, and who was to use astronomical tables to establish the date when Jesus died on the cross. His result of 3 April 33 CE, though unorthodox at the time, continues to be viewed as plausible by many contemporary scholars. In the following century, the application of astronomy to history was pursued by authors such as the Swabian astronomer Heinrich Selder, who used Ptolemy’s eclipses to bring order into biblical, but also ancient Greek and Near Eastern, chronology. Others, like the Benedictine monk Walter Odington (Summa de etate mundi, 1308/16) and the Oxford astrologer John Ashenden (Summa iudicialis de accidentibus mundi, 1347/48), tried to tame the timeline by bringing in assumptions of an astrological, as opposed to just astronomical, nature. In Odington’s case, his efforts to extort the age of the world from a calculation based on 360-year planetary circles proved irreconcilable with biblical chronology, prompting him to boldly surmise that the numbers encountered in Scripture had to be read in an allegorical rather than a plain historical way—an idea that stands in striking contrast to the assumptions made by present-day Young Earth Creationists.

Seven centuries down the line, we possess sufficient hindsight to discern more or less exactly where authors such as Giles of Lessines and Walter Odington went wrong or, conversely, where their arguments produced results of lasting validity. More so than any particular date proposed in these medieval texts, what remains unchanged is the fundamental soundness of their insight that the predictive capacities of natural science can furnish historical chronology with the sort of security its conclusions would otherwise be lacking. To this day, astronomical phenomena, from comets and the positions of stars to the intervals revealed by ancient eclipses, remain absolutely essential to the basic grid of ancient dates displayed in our reference works. In addition, the range of possibilities has been greatly expanded by novel chronological tools such as stratigraphy, radiometric dating, dendrochronology, and the study of Greenland ice cores.

Owing to these methodological developments, our conventional chronology of the past three millennia rests on such a solid basis that twenty- and twenty-first century attempts to subvert it have been staged almost exclusively from the fringes of respectable scholarship. One of the few flavors of such chronology revisionism to have captivated a larger audience is Heribert Illig’s so-called phantom time hypothesis, which argues for the fictitious character of the period we usually refer to as the Early Middle Ages. If Illig is right, which is more than unlikely, the reign of Charles the Great and all the other persons and events historians of medieval Europe assign to the years 614–911 were no more than an invention, retroactively inserted into the historical record by a cabal of powerful men involving the Holy Roman Emperor Otto III (980–1002) and Pope Silvester II (999–1003).

Beyond the tiresome hermeneutics of suspicion and outright falsehoods that pervade the hypothesis propagated by Illig and his followers lies a valuable reminder to the effect that historians should, at least on occasion, try to assure themselves of the foundations on which their accepted narratives rest. In a sense, the revisionists are indeed correct in assuming that some of these foundations can be unearthed deep in the Middle Ages. Their actual shape, of course, looks very different from what they would have us believe.

C. Philipp E. Nothaft is a post-doctoral research fellow at All Souls College, Oxford. He is the author of “Walter Odington’s De etate mundi and the Pursuit of a Scientific Chronology in Medieval England,” which appears in the April 2016 issue of the Journal of the History of Ideas.

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