1. Representative and unique: why St John's 17 looks the way it does.
2. The historical development of the computus manuscript.
3. Reconstructing exemplars.
3.1 Byrhtferth's computus
3.2 The Tiberius-Leofric computus
3.3 The Winchester computus

1. Representative and unique: why St John's 17 looks the way it does.

MS 17 is a representative of a distinctive type of compilation: the computus manuscript. The many hundreds of computus manuscripts surviving from the medieval period share a certain family resemblance, but the historical evolution of the genre also produced sub-families with distinctive traits.1 MS 17 displays all the fundamental features of the computus compilation, as well several layers of its transformation from the age of Bede to the 11th century. Finally, it bears the imprint of a computus manuscript once owned by Byrhtferth of Ramsey.

The irreducible core of the computus anthology is the two essential tables on which Christian time-reckoning depended: the Julian calendar, which permitted the registry of fixed anniversaries and the establishing of the sequence of weekdays in any given year; and the Paschal table, which furnished the date of Easter for a discrete sequence of years. Both of these master-tables carried dependent materials in its train. The calendar requires either formulae (argumenta) or key-letter tables in order to translate its generic dates into year-specific data such as the dates of Sunday, or the phase of the moon, and these tables might be accompanied by instructions (canones). The Paschal table is in principal self-contained, but in practice was accompanied by argumenta for the data in each of its columns, as well as historic documents explaining its principles: in the case of MS 17, these are the two letters of Dionysius Exiguus, who successfully adapted the Alexandrian 19-year Paschal cycle for the Latin church.

Besides these supplementary items, computus manuscripts as early as Bede's time came to serve as repositories for information on other subjects connected with the reckoning of time. Some of these, such as astronomy and mathematics, can be considered background materials, but other types of lore became attached to the computistical core through a sort of associative process: medicine, because diagnostic and therapies were governed by seasonal and lunar considerations, or prosody, because it measures the temporal dimension of speech. Bede himself acknowledged and encouraged this encyclopedic trend by incorporating into De temporum ratione elements of cosmography (especially chapters 25-34) and medicine (ch. 35), to say nothing of a significant body of history (ch. 66).

MS 17 represents this broadly "encyclopedic" strain of computus manuscript, but it is also the product of specific trends which shaped the content and arrangement of the anthology in the centuries following Bede. These forces established distinctive families of computus anthologies, where groups of texts, or tables of a characteristic type, were transmitted from exemplar to copy. However, these families could also interbreed, because the computus manuscript favours an open, album-like structure which can absorb and shed non-core materials with ease. MS 17's heritage incorporates the computus manuscript of Byrhtferth of Ramsey, as in so doing, the computus of Abbo of Fleury that lay behind it; but it also includes Abbonian material not found in Byrhtferth's writings or the other manuscripts connected to him. As well, it picked up items from two non-Abbonian English lineages, as well as older Carolingian anthologies.

2. The historical development of the computus manuscript.

The oldest computus manuscripts, represented by the Sirmond manuscript (Oxford, Bodelian Library Bodley 309) whose avatar was used by Bede himself, might be called "scholarly" in character,2 though it would perhaps be more accurate to designate them as "controversial" or "polemical." Before the time of Bede, the production of computistical literature was driven by the need to prove the validity of a particular set of criteria for determining Easter, and the workability of a specific Paschal table. Hence the Sirmond volume contains a substantial dossier of letters and documents justifying the Alexandrian cycle, and attacking other systems.3 But these polemical intentions entailed teaching the preferred cycle, as well as providing rules for constructing and extending it. Argumenta and didactic tracts, often in dialogue form, responded to these needs, and can also be found in the Sirmond volume. Traces of this archaic controversial-didactic anthology in MS 17 include the letters of Dionysius Exiguus defending his Paschal table, the argumenta accompanying the table, and the textbooks of Bede and Helperic.

With the publication of Bede's De temporum ratione, the controversies over Easter effectively came to an end in the West. With the emergence of the Carolingian kingdom in Francia, computus assumed a new role, and the form of the manuscript was modified accordingly. Carolingian computus manuscripts can be described as "scholastic" in character. Charlemagne and his successors were convinced that the stability and success of their realm depended upon pure and correct worship, and their educational reforms aimed at fostering this through correct Latinity, orthodox reading, and uniform liturgical practice. The reform program of the Admonitio generalis of 789 laid out a vocational curriculum of reading (psalmos, libros catholicos), writing (notas), chant (cantus) and computus.4 This elevated computus into a subject of wide-spread and formal instruction, at least in theory. Charlemagne was personally interest in "computing and the science of the stars", and exchanged letters with Alcuin on these subjects.5 Missi were enjoined to report on the level of computus expertise in the ecclesiastical establishments they visited.6 At the same time, the court focused on promulgating an authoritative form of the calendar, and Arno Borst has argued that a critical feature of this reformed calendar was the inclusion of computistical and astronomical information.7 Though Borst's views have not won universal acceptance,8 there is no doubt that the Carolingian period saw a immense proliferation of computus manuscripts. Carolingian computus manuscripts also exhibit a marked trend towards expanding the encyclopedic penumbra, particularly in the domains of astronomy and cosmology. Texts like the Aratus latinus, the astronomy of Hyginus, and excepts from Pliny, Martianus Capella, and Macrobius joined the computistical core,9 and in the case of one family of deluxe manuscripts known as the "Aachen encyclopedia of 809", came to dominate it.10 Carolingian educators like Hrabanus Maurus, eager to revive what they imagined to be the ancient program of the Liberal Arts, identified computus with astronomia. The computus manuscript was on its way to becoming an encyclopedia of the quadrivium.11 This development is discussed in the Overview to MS 17's Cosmographical Anthology.

Another feature of the Carolingian computus was the proliferation of key-letters within the calendar, and tables for decoding them. This proliferation accelerated in the 10th century, under the influence of Abbo of Fleury, whose own computus compilations are albums of ingenious schemata, rotae, and reference tables. Abbo was also interested in new trends in mathematics, notably the revival of the Roman abacus. The Abbonian computus manuscript is discussed at greater length in the Overviews of MS 17's Calendar, Computus Texts and Tables II, and the Cosmographical Anthology. Here it suffices to point out that its key features: (a) a calendar with eight columns of key-letters, accompanied by a suite of elaborate and original tables; (2) Abbo's own perpetual calendar, the Ephemerida Abbonis ; and (3) a series of original astronomical tracts , not all of which are found in all Abbonian computus manuscripts.12 With Abbo, the computus manuscript enters a new phase, as a technical manual.

3. Reconstructing Exemplars.

The core of MS 17 is a computus of the type developed by Abbo of Fleury. In particular, it appears to be an Abbonian collection assembled in large part by Byrhtferth of Ramsey, to which were added (possibly by Byrhtferth himself) materials from two non-Abbonian strains of English computus manuscript: the "Leofric-Tiberius" type, and the "Winchester" type.

3.1 Byrhtferth's computus

Heinrich Henel was the first to recognize that Byrhtferth's Enchiridion or Manual is actually a commentary on a computus manuscript; André Van de Vyver later identified MS 17 as a copy of very compilation Byrhtferth used.13 Later, the Peterborough computus and Winchcombe computus , close relatives of MS 17, emerged as additional witnesses to the shape of Byrhtferth's codex. The shape of this codex has been reconstructed on the basis of the three manuscripts by Peter Baker and Michael Lapidge.14 They begin from the premise that the materials on fols. 13v-41r of MS 17 are overwhelmingly Abbonian; since Byrhtferth's computus was Abbonian, the materials must have come to MS 17 from Byrhtferth's exemplar. A reverse logic is then employed to argue that since MS 17's mappamundi and taxonomy of philosophy schema are found in the Peterborough computus, they must have been in Byrhtferth's manuscript, even though Byrhtferth shows no familiarity with these materials.15 Non-Abbonian materials are accounted for by positing that Byrhtferth himself expanded his Abbonian compilation with materials from manuscripts of the "Leofric-Tiberius" and "Winchester" families (see below), and even from unidentified Carolingian or earlier sources. To all of these, Byrhtferth added his own original material, whose traces in MS 17 include Byrhtferth's Diagram, his Proemium , the gloss on the saltus lunae on fols. 15r-v), the metrical portions of the martyrology, the Pachomian hand and its text , the paradigm Paschal table on fols. 29r-v, and the four criteria for finding Easter on fol. 34r.16 MS 17's copy of Helperic's De computo is also derived from Byrhtferth. Baker and Lapidge's reconstruction, while persuasive in its broad outlines, sometimes breaks down on the details; moreover, it is based on the silent assumption that the scribes of MS 17 copied Byrhtferth's computus manuscript tel quel.

This table summarizes their reconstruction of the Byrhtferthian ancestor of MS 17. The reader is directed to the commentaries on individual items, where any arguments for and against Byrhtferth's direct responsibility for the item in question will be laid out. The first column contains the reference number in Appendix A of Baker and Lapidge's edition of Byrhtferth's Enchiridion. The second column contain the folio(s) in MS 17, and the third identifies the item.

Number Folio(s) Item
1 6r Mappamundi
2 7r Taxonomy of knowledge
3 7v Byrhtferth's Diagram
4 12v-13r Byrhtferth's Proemium
5-6 13v Computus graecorum
7 14r Computus poetry: Me legat annales
8 14r Computus poetry: Bissena mensium
9 14r Computus poetry: Ianus et Octimber
10 14r Computus poetry: September semper quinis
11 14r-v Computus poetry: Bissex signifere
12 14v Computus poetry: Prima dies Phebi
13 14v-15r Embolisms
14 15r-v Saltus lunae
15 16r-21v Calendar: see especially Greek, Hebrew, Egyptian and English month names, Length of the month, Martyrology, Key letters, materials unique to the months of February, March, and December.
16 22r Dominical letters table
17 22r-v Litterae punctatae table
18 22v-23r Lunar letters A-V, A.--I.
19 23r Criteria for moveable feasts
20 23r-v Pagina regularis
21 24r Lunar-zodiac table
22 24v Ember fasts, AEIOV lunar letters table
23-24 25r-26r Ephemerida Abbonis
25 26v Lunar letters A-K table
26 27r Rota of lunar epacts
27 27r Rota of feria for kalends
28 28r Paschal hand
29 28r Legend of Pachomius
30 28r-v Termini of moveable feasts
31 28v-29v Paradigm Paschal table
32 30r-31v Tabula Dionysii , Key Letter tables
33 32r-v Feria of terminus tables
34 33r Computus memoranda
35 33v Perpetual calendar 1
36 34r Perpetual calendar 2
37 34r Easter criteria
39 34v Multiplication and division tables
40 35r Abbo's abacus; 7 and 59 times table
41 35v Solstices and equinoxes; Synodic month
42-43 36r Hours of moonlight
44 36r-v Egyptian months
45 37r Horologia
46 37v Isidore on the planets
47 37v-39r Abbo on the planets, Planetary evagations; Abbo on the Moon + glosses.
48 39r-v Isidore on the elements
49 39v Macrobius on "gravity"
50 40r Isidore on the climates
51 40r The five zones
52-53 40v Isidore on the winds
54 41r Sphere of life and death 2

3.2 The Tiberius-Leofric computus

Some of the elements of MS 17's computistical core are characteristic of a family of late Anglo-Saxon computus compilations typified by British Library Cotton Tiberius B.V and the Leofric Missal. Others in this group include British Library Cotton Galba A.XVIII, Cambridge University Library Kk.5.32, Cambridge Corpus Christi College 422, British Library Cotton Julius A.VI, Bodleian Library Digby 81, Bodleian Library Hatton 113 and the Missal of Robert of Jumièges, a manuscript particularly close to Tiberius and Leofric. (xlviii) Much of the computus memoranda on fol. 33r, for example, is Tiberius-Leofric material.

3.3 The Winchester computus

A rather more prominent influence on MS 17 was exerted by a type of computus manuscript initially created in Winchester around the year 978. One of the compiler's principal resources was the Tiberius-Leofric computus. The influence of Abbo is minimal, but there is a significant presence of older Carolingian material. This Winchester family includes the "Prayerbook of Aeflwine," Cambridge Trinity College R.15.32 pp. 13-36, British Library Cotton Vitellius E.XVIII, British Library Arundel 60, and British Library Cotton Tiberius C.VI fols. 2r-7r. Cambridge Corpus Christi College MSS 9 and 391 (the "Portiforium of St Wulfstan") represent a Worcester recension, which Baker and Lapidge argue Byrhtferth used. 17

The Winchester computus lies behind MS 17's Computus graecorum , as well as the suite of tables between fols. 27r-28v: the rota of lunar epacts, the rota of the feria of the kalends, the Legend of Pachomius and its application to other moveable feasts, and the table of termini of moveable feasts.

1 Wallis 1990.

2 Baker and Lapidge 1995, xli.

3 Wallis 1999, lxxii-lxxix; Jones 1937; Ó Cróinín 1983.

4 Ed. A. Boretius, Capitularia regum francorum, MGH Leges (Quarto), 2 (1883), 1.59-60.

5 Einhard [25 pp. 76-77]; Alcuin, letters 145 on the saltus lunae, and 148 on the calculation of the zodiacal signs, ed. Ernst Dümmler, Epistolae Carolini aevi, MGH Epistolae 4 (1895), 2.231-235 and 237-241. On Alcuin and computus, see Springsfeld 2002.

6 Capitularia regum francorum, MGH Leges (Quarto), 2 (1883), 1.237.

7 Borst 1998; Borst 2001.

8 See the work of Englisch 2002 and Meyvaert 2002, and response in Borst .

9 McCluskey 1998; S. McCluskey, "Astronomies in the Latin West from the fifth to the Ninth Centuries," in Science in Western and Eastern Civilization in Carolingian Times , 139-160; Bruce Eastwood, "The Astronomies of Pliny, Martianus Capella and Isidore of Seville in the Carolingian World," in Science in Western and Eastern Civilization in Carolingian Times , 162-168.

10 Arno Borst, "Alkuin und die Enzyklopädie von 809," in Science in Western and Eastern Civilization in Carolingian Times , 53-75; Anton von Euw, "Die künstlerische Gestaltung der astronomischen und komputistischen Handscriften des Westens," in Science in Western and Eastern Civilization in Carolingian Times , 251-268.

11 Wallis 1999, lxxxix-xci.

12 Baker and Lapidge 1995, xliii-xliv.

13 Henel 1934, 5-34; Van de Vyver 1935, 144-145. Van de Vyver's insight was anticipated by Singer and Singer 1917-1919, 47-51, and Forsey 1928.

14 Baker and Lapidge 1995, Appendix A.

15 Baker and Lapidge 1995, lvii.

16 Baker and Lapidge 1995, lviii-lx.

17 Baker and Lapidge 1995, xlviii-lii.