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Ketton, Robert oflocked

(fl. 1141–1157)
  • Charles Burnett

Ketton, Robert of (fl. 1141–1157), astronomer and translator, is almost certainly identifiable with Robert, archdeacon of Pamplona (fl. 1145–1157): both are attested in Spain in the middle decades of the twelfth century. He often appears in the sources with the toponym Ketenensis, which is usually identified with Ketton in Rutland. A third Robert, a writer and translator of scientific works, also active in Spain at that time and commonly considered to have been identical with the first two Roberts, was in fact a different man, as indicated by his different toponym, Robert of Chester [see below].

A Rodbertus Ketenensis collaborated with Hermann of Carinthia (fl. 1138–43) in translating Arabic texts. Their project, as explained by Robert himself, in the preface to his translation of al-Kindi's Judicia ('Astrological judgements'), was to study Euclid's Elements, Theodosius's Spherica, and 'a book of proportions', as preparation for understanding Ptolemy's Almagest—all texts that they would have read in Arabic or in translation from Arabic. Moreover Robert, in a letter to Peter the Venerable, abbot of Cluny, written in 1143, promised:

a celestial gift which embraces within itself the whole of science … revealing most accurately, according to number, proportion and measure, all the celestial circles and their quantities, orders and conditions, and, finally, all the various movements of the stars, and their effects and natures and everything else of this kind.

Patrologia Latina, 189.660

The form Rodbertus Ketenensis is confirmed by Hermann's naming him in this way in the preface to his translation of Ptolemy's Planisphere (1 June 1143), which he addresses to Thierry, chancellor of Chartres, the well-known educator. Elsewhere in his translation of this work Hermann indicates that Robert has made available Albeteni, which would be the canons and tables of al-Battani, the tenth-century astronomer from Baghdad. Confirmation that Hermann and Robert were working together comes from Peter the Venerable, who met them on the banks of the Ebro in 1141 (probably at Logroño) and persuaded them to depart from their usual study of 'astronomy and geometry' in order to translate some texts concerning Islam. While two texts dedicated by Hermann to Robert are extant (his translation of Abu Ma'shar's Maius introductorium of 1140 and his original cosmological work of 1143, De essentiis), both expressing his friendship with, and very close dependence on, Robert, there is only one text of Robert that is clearly the fruit of this collaboration: the Judicia of al-Kindi. In his preface to this work Robert expresses his reluctance to translate a work of astrology, when his real interest is in geometry and astronomy, but states that he has undertaken the work on Hermann's request lest their friendship should grow cold. Most of the manuscripts of this work state, erroneously, that the translation was made 'per Robertum Anglicum Anno Domini 1272' (probably out of confusion with Robert the Englishman (c. 1271)); however, a thirteenth-century English manuscript in the British Library (BL, Cotton MS Appendix vi, fol. 109r) gives the name of the translator as 'Roberus [sic] de Ketene'. It is possible that another text arose out of Robert and Hermann's work together: that is the version of Euclid's Elements, hitherto known as the 'Adelard II', since its earliest manuscript is the copy included in the Heptateuchon of Thierry of Chartres, who, as already mentioned, received the dedication of one of Hermann's translations, and Robert mentions 'Euclid' specifically as a text that Hermann and he had studied.

Robert's translations of Islamic material commissioned by Peter the Venerable (known as the Toledan Collection) are well documented. While Hermann translated texts Liber generation is Mahumet ('On the generation of Muhammad') and Doctrina Mahumet ('The teaching of Muhammad'), Robert translated Chronica mendosa Saracenorum—a brief history of the early caliphs—and the centrepiece of the collection, the Koran itself. Robert's translation of the Koran, apparently made with the assistance of a certain Muhammad, is the earliest translation of the Koran into any language. It is quite a free rendering of the Arabic, and breaks up the (ṣūrat (‘chapters’)) in a different way from the original. It was used by Peter the Venerable to compile his Summa against the Saracens, and was frequently copied. The entire Toledan Collection was printed in 1543 in Basel by Theodore Bibliander, with a preface by Philip Melanchthon.

That this Rodbertus Ketenensis is the 'magister Rodbertus' who appears as archdeacon of Pamplona in charters at Pamplona in 1145, 1147, 1149, 1151, and at Barcelona in 1152, and as canon of Tudela in 1157, is indicated only by the joint testimonies of Peter the Venerable and his secretary, Pierre de Poitiers. The latter, ‘editing’ the collection of Islamic texts for the abbot of Cluny in 1143 or 1144, mentions the solution of a problem concerning the Islamic faith in the following terms: 'It is stated thus in the Alcoran, just as I myself heard for certain in Spain, both from Peter of Toledo, whose companion I was in translating [Pseudo-Alkindi's Apologia], and from Robert, now archdeacon of Pamplona' (Patrologia Latina, 189.661). Peter the Venerable, in a letter accompanying the Islamic material sent to Bernard of Clairvaux in the spring or summer of 1144, refers to the translator 'Roberto Ketenensi de Anglia, qui nunc Pampilonensis ecclesiae archidiaconus est' ('Robert Ketenensis of England, who is now archdeacon of the church of Pamplona'; Kritzeck, 212). Unless Peter the Venerable, misled by a statement of his secretary, confused two Roberts, it would seem that Robert of Ketton became archdeacon of Pamplona shortly before 1144. Unfortunately, none of the documents from Pamplona or Tudela give Robert the archdeacon any cognomen, though almost all of them describe him as magister. It is not implausible that a scholar of the arts (which included geometry and astronomy) would progress to theology and a position in the church, as Alexander Neckam (d. 1217) and Robert Grosseteste (d. 1253) were destined to do later. Master Robert, archdeacon of Pamplona, had a distinguished, if turbulent, career. His archdeaconry was probably that of Valdonsella, whose chief town was Uncastillo, and which was disputed between Navarre and Aragon. On 1 July 1149 he drew up a peace treaty between the king of Navarre, García V (r. 1134–50) and the Aragonese party, lead by Raymond-Berengar (IV), count of Barcelona—this important diplomatic service was acknowledged by the pope, Eugenius III. In 1151 he was the delegate of the bishop of Pamplona in a territorial dispute with the bishop of Saragossa. Closer to home Robert is found leading a rebellion of the clergy against their own bishop, Lope (Lupus), which was patched up temporarily. However, relations between him and Bishop Lope eventually reached such a point that he broke with him altogether and sided with the party of the new king of Navarre, Sancho VI (the Wise) (r. 1150–94). Presumably through the king's agency, he acquired in exchange for his lost archdeaconship the canonry in the church of Tudela, in the possession of which he is last recorded (1157). On the one hand, Robert's education would fit him well for the roles of diplomat, royal adviser, and redactor of official documents which he evidently fulfilled. On the other hand, since in the team translating Arabic geometrical and astronomical tables he was clearly the senior partner, with contacts in high places, he may already have been destined for a career in the church (there is no evidence for Hermann's preferment). The partnership between Robert of Ketton and Hermann of Carinthia would be parallel to those between other churchmen and ‘professional’ translators or scientists in Spain, such as Dominicus Gundissalinus, archdeacon of Segovia, and John of Spain, or Mauritius, archdeacon of Toledo, and Marco de Toledo. Robert of Chester (fl. 1144–1150), scientific writer and translator, has often been confused with the former. Robert of Ketton's progression from scientist to churchman would be unproblematic were it not for the fact that from 1144 onwards, there are further works in Arabic science attributed to a Robert, who has been assumed to be the same as Robert of Ketton. However, these works are attributed not to a Ketenensis but rather to a Cestrensis (of Chester). These texts are: translations of an alchemical work called Liber Morieni with a Praefatio castrensis and the date '11 Feb., era 1182' (1144), and of al-Khwarizmi's Algebra, made by Robertus Cestrensis in Segovia in 1145; an original treatise on the construction of the universal astrolabe written by Robertus Cestrensis in London in 1147; astronomical tables of 1150 or 1170 for the meridian of London 'composed by Robert of Chester' and allegedly based on the tables of al-Battani, which are the second part of further unattributed astronomical tables based on the meridian of Toledo; an original treatise on the use of the planispheric astrolabe; and a revision of Adelard of Bath's version of the astronomical tables of al-Khwarizmi 'arranged in order by Robert of Chester' of unknown date, but including the corrections required for the displacement of the meridian of reference to London. Given that Robert's English base appears to have been London at the time when this was the centre of King Stephen's power, it is possible that he was also responsible for the set of political horoscopes drawn up mainly for the years 1150 and 1151 by a partisan of the king. He may have written a work on rhythmomachy if he is the Castrensis referred to as a theoretician of the game in C. Buxerius's Nobilissimus et antiquissimus ludus Pythagoreus (1556); (fol. 42r)). Finally, he may have translated from Arabic Ptolemy's Tetrabiblos ('Four books on astrology') in which the anonymous translator speaks of 'Maior Britannia in qua patria nostra excestria' ('greater Britain in which our fatherland is Chester'; Herzog August Bibliothek, Wolfenbüttel, MS Gud. lat. 147), though the date given to the translation, 29 August 1206 (confirmed by the addition of its Arabic equivalent), argues against the attribution.

The manuscripts, several of which fall within the twelfth century, are unanimous in calling this Robert Cestrensis (or Castrensis). It would seem unlikely, therefore, that a scribal confusion between ‘Ketenensis’ and ‘Cestrensis’ is involved, as Charles Homer Haskins suggested (Haskins, 120). Either Robert changed his name after completing his translation of the Islamic material, as Richard Lemay has claimed, or Robert of Ketton and Robert of Chester are two different people, as claimed most recently by Richard Southern. The arguments in favour of their identity are that the translations of both Roberts are characterized by a tendency to abbreviate, to write idiomatic Latin, and to avoid Arabisms. Most specifically, both Roberts had some involvement with astronomical tables attributed to al-Battani. However, grounds for separating the two Roberts are strong. Robert of Chester is never associated with Hermann of Carinthia. In the earliest text attributed to Castrensis—the Liber Morieni—the translator apologizes for his immature talent and his lack of Latin, as if this were his first attempt at a translation. The translations of Robert of Chester do not seem to fit the rigorous mathematical programme outlined by Robert of Ketton: they do not include Theodosius's Spherics, 'a book of proportions', or the Almagest, or, for that matter, any work on geometry as preparatory for the study of astronomy, but, on the other hand, take in alchemy and algebra, which have little bearing on astronomy; the translations of alchemical and algebraic texts are apparently the earliest in those subjects. The places of composition of Robert of Chester's works are not in the north of Spain, but in Segovia and London, and his activity lasts until later in the century (if the tables containing the date 1170 are his). If Robert of Ketton follows an expected career structure, progressing from the liberal arts to theology and the church, Robert of Chester's career too is familiar. Like Adelard of Bath (fl. c.1080–1150), Alfred of Shareshill (fl. 1214×1222), and Daniel of Morley (d. 1210), he went abroad to study, but then returned to England to put the fruits of his research at the disposal of his fellow citizens.


  • C. H. Haskins, Studies in the history of mediaeval science, 2nd edn (1927), 44–9, 120–3
  • J. G. Gaztambide, Historia de los obispos de Pamplona, 1 (Pamplona, 1979), 391–432
  • R. W. Southern, Robert Grosseteste: the growth of an English mind in medieval Europe, 2nd edn (1992), xlvii-xlix
  • R. P. Mercier, ‘Astronomical tables in the twelfth century’, Adelard of Bath: an English scientist and Arabist of the early twelfth century, ed. C. Burnett (1987), 87–119
  • J. D. North, ‘Some Norman horoscopes’, Adelard of Bath: an English scientist and Arabist of the early twelfth century, ed. C. Burnett (1987), 147–61 [here attributed tentatively to Adelard of Bath]
  • P. Kunitzsch, Glossar der arabischen Fachausdrücke in der mittelalterlichen europäischen Astrolabliteratur, Nachrichten der Akademie der Wissenschaften in Göttingen I. Philologisch-historische Klasse, 1982, 11 (1983), 489–92
  • R. Lemay, ‘L'authenticité de la préface de Robert de Chester à sa traduction du Morienus (1144)’, Chrysopœia, 4 (1991), 3–32
  • Robert of Chester's (?) redaction of Euclid's ‘Elements’, the so-called Adelard II version, ed. H. L. L. Busard and M. Folkerts, 1 (1992), 22–31
  • ‘Petrus Cluniancensis: epistolarum libri sex’, Patrologia Latina, 189 (1854) [Peter the Venerable, Letters]
  • J. Kritzeck, Peter the Venerable and Islam (1964)


  • BL, Cotton MS Appendix vi, fol. 109v
  • Herzog August Bibliothek, Wolfenbüttel, MS Gud. lat. 147