Perhaps nothing in Christian history has caused more controversy than the date of Easter. We hear from Eusebius of controversy in the second century; Eastern and Western Christendom are still divided over the question. More recent suggestions for a fixed Easter, say on the second Sunday of April, despite the occasional enthusiastic announcements from one or another (Western) hierarch, could only complicate further this history of division. The English term, Easter, disguises the fact that the Feast of the Resurrection of Christ is, in fact, the Christian Passover, an identification made clearer by the use of the Greek term for either feast: Pascha. The origins of the Christian celebration of Pascha are shrouded in mystery. What seems most likely is that by the second century many (even most) Christians simply gathered together weekly to celebrate their faith in Christ on Sundays. However, in Asia Minor, Christians, claiming the authority of the Apostle John, celebrated the Christian Pascha at the same time as the Jewish Passover, that is, on the night of 14/15 Nisan, the first month of the Jewish Year (according to one reckoning), that marks the beginning of Spring—whatever day of the week 14 Nisan occurred (Christians who followed this practice came to be known as Quartodecimans, that is, ‘Fourteen-ers’). The invocation of the name of John in this context may have something to do with the fact that in the fourth Gospel Jesus’ death on the cross occurs simultaneously with the sacrifice of the Passover, or Paschal, lamb in the Temple in Jerusalem, whereas in the other three Gospels Jesus’ last meal with his disciples is the Passover meal itself, on the evening after the offering of the Paschal lamb; but if so, it is not clear how. These conflicting ways of celebrating the death and resurrection of Christ led eventually to controversy, which is reported by Eusebius in his Church History (in a somewhat confusing manner, because either Eusebius did not know, or did not want us to know, the nature and extent of the division among second-century Christians).
Reconciliation, or compromise, was reached by agreeing to celebrate the Christian Passover, the yearly memorial of the death and resurrection of Christ, on the first Sunday after 14 Nisan, itself understood to be the occasion of the first full moon after the Spring Equinox, an agreement confirmed more than a century later at the first Œcumenical Council, held in Nicaea in 325. This agreed date—the first Sunday after the first full moon after the spring equinox—seeks to bring into some kind of conjunction the three cycles that measure out the sequence of time through which we live: the week of seven days, the month governed by the circuit of the moon around the earth, and the year consisting of the seasons of spring, summer, autumn, and winter (which we, from our post-Copernican heliocentric perspective, call the solar cycle, governed by the circuit of the earth around the sun). These cycles, inconveniently, do not fit into each other: the lunar month is a little more than four weeks, the solar year somewhat more than twelve lunar months. If one is going to keep them more or less in conjunction, then some adjustment is required. Of course, one does not have to do this: Muslims have a year of twelve lunar months, but this means that there is no correspondence between the months and the seasons of the year, so that Ramadan, the month of the yearly fast, can occur at any time during the year. Jews and, following them, Christians value the linking of the annual seasons and the sequence of the months. For Christians, following again the Jews, fixing Pascha on the first Sunday after the first full moon after the spring equinox secures this link between the seasons and the months, so that Pascha always occurs in spring. Traditionally the Jews made sure that Nisan coincided with the beginning of spring by intercalating a lunar month every so often, so as to prevent Nisan falling at the end of winter. The beginning of Nisan was established by observation—of the tiny sliver of the New Moon closest to the Spring Equinox. It looks as if the Quartodecimans followed this practice, but as the Christian year developed, with a fast before Pascha lasting from a few days to a week and eventually to forty days, it became necessary to know the date of the Paschal full moon long before the fourteen days provided by observation of the New Moon of Pascha. The third century saw several attempts to calculate when Pascha would fall each year. Nowadays this could be calculated by astronomical means; but in the third century, and for many centuries thereafter, recourse had to be had to calendars, and from them to work out a sequence of dates for the years to come.
The question of the date of Easter was raised at the First Œcumenical Council of Nicaea; it was decided that Alexandria, with its renowned astronomical tradition, should provide the date, and thereafter the paschal letters of the patriarchs of Alexandria, issued early in the year, provided this information for the whole church. (We only have a report of this decision, not the details, for none of the surviving canons addresses this issue.) This did not stop other churches going their own way, especially if they thought that their own calculations were the same as Alexandria’s. So in 387, Ambrose of Milan issued a letter in which he departed from the Roman date, having discovered that it differed from the Alexandrian one.
In the book under review, Professor Mosshammer provides a new critical edition, with translation and notes, of a crucial witness to this tradition, The Prologues on Easter of Theophilus of Alexandria and [Cyril] (the square brackets round Cyril indicate that what we have from Cyril’s hand is a list of paschal data for 95 years, and a prologue written in his name, but not by him). These texts witness to the role of the Alexandrian bishop in determining the date of Easter, assigned to him by Nicaea I. They survive in Latin versions, themselves witnesses to the importance of the question of the date of Easter for the Western Church, not least for such as Dionysius Exiguus in the sixth century and Bede in the eighth. Mosshammer’s critical text draws on manuscripts not hitherto known to scholars, and his translation and full commentary explain the knotty problems these prologues were trying to solve.
Professor Mosshammer is uniquely qualified to elucidate all this, for he himself, in an earlier monograph, The Easter Computus and the Origins of the Christian Era (2008), discussed with serene authority the early Christian methods for calculating the date of Easter, in the process dispelling a great deal of accumulated scholarly (and not-so-scholarly) misinformation. To do more than refer to the detail elucidated by Professor Mosshammer in this book would require a review not much shorter than the book itself, but some indication of the kind of issues raised can be seen from a short text, Ratio Solis vel Lunae (an account of the sun and moon), also included in this volume, which sets out in four brief paragraphs the problems involved in bringing the cycles of the sun and the moon into alignment. It begins with an intriguing assertion: ‘The 8 Kalends of April (25 March) is one equinox, and on the 8 Kalends July (24 June), the birthdate of St John, is one solstice. On the 8 Kalends October (24 September), the day of St John’s beheading, is the other equinox. And on the 8 Kalends January (25 December), the birthdate of our Lord Jesus Christ, is the other solstice’. This brings out the concern to bring the seasons and the feasts of the Christian year into conjunction (to regard 24 September as the date of St John’s beheading, rather than his conception, is a distinctively Spanish feature, indicating unmistakeably the provenance of this text). 25 March is the (Roman) date of the spring equinox, but also of the conception of Christ (the Feast of the Annunciation to the Virgin Mary) and, many Christians believed, of his death. It was argued by the great church historian, Duchesne, that it is this conjunction between the date of the creation of the world (at the spring equinox, when else?), the conception of Christ (‘the crowning moment of our salvation’, as a Byzantine text for the Feast of the Annunciation has it), and the death of Christ that determined the date of the Feast of the Annunciation, and thereby the date of the Feast of Christ’s Nativity, nine months later: a conjecture that has only gained in strength in the last century. The complicated issues that Mosshammer explains so lucidly in his commentaries were so important, for their significance is not just religious and calendrical, but for Late Antiquity reached beyond that, into the structure of the cosmos itself.