Today, three mediaeval Latin translations of the Almagest are known – two made from Arabic and one from Greek. All three translations were produced within the same relatively short period of time during the mid- and late-twelfth century, but each version was made independently from the others, under different conditions and in a different part of the Mediterranean world. Furthermore, each of the versions is based on a different source tradition and had varying degrees of influence in Europe.
The earliest Latin version of the Almagest was made in the Crusader states, in the principality of Antioch, in the late first half of the twelfth century. It is based on an Arabic tradition of the Almagest which is attributed to the ninth-century mathematician Thābit ibn Qurrah and of which only fragments are known today. The Latin translator, Ebdelmessie Wintoniensis (a Latinized form of ʿAbd al-Masīḥ of Winchester), may have been a local Christian Arab, whereas his text is related to the works of another translator from Arabic, Stephen of Antioch. The connection suggests that coordinated Arabic-Latin translation activities were taking place in Syria, where Western scholars had the chance to collaborate with local experts. Ebdelmessie's translation closely reproduces Arabic formulations, but is nevertheless very readable and technically accurate. Innovations in this text include a consistent Latin terminology which avoids any transliterations of Arabic technical terms as well as a unique system of numerals. Despite its high quality, Ebdelmessie's translation of the Almagest did not find popularity in Europe. It survived only in a single incomplete copy from around AD 1300 (now in Dresden) and no influence of the text on other mediaeval authors has been identified.
Ebdelmessie's version of the Almagest was followed by a translation from Greek, which was made in Sicily, presumably in the early 1160s. The translator tells us that he had come from outside Sicily to the Norman court at Palermo after he had heard that a copy of the Almagest in Greek had arrived there. Reception of this second Latin Almagest can be traced up to the fourteenth century, but its influence, which seems to have been strongest in Italy, remained again very limited. Three manuscripts of the text are extant today in Rome and Florence; Ptolemy's preface according to this version also appears in a fourth manuscript now in Wolfenbüttel.
The translation that would soon become the standard reference for astronomical studies in Europe was again made from Arabic and published, with continuing modifications, between AD 1175 and AD 1185. Its author, Gerard of Cremona, must have had at least basic notions of the Almagest when he was driven by his ‘love for the Almagest’ to move to Toledo, in today's central Spain, in order to produce a Latin version of Ptolemy's work. Toledo had been a centre of Arabic learning, which fell into Christian hands in AD 1085. Aside from a large amount of Arabic manuscripts that were accessible in Toledo, Gerard received important help for his translation from a local Mozarab (i.e. an Arabised Christian). In contrast to the previous two translations, Gerard's version of the Almagest quickly spread through Western Europe. More than 300 years after its production, in AD 1515, it also became the first version of the Almagest to appear in print.
Gerard's Latin follows the Arabic wording extremely closely, in that many passages of the translation are hard to understand due to frequent Arabisms. The literalness of the translation reveals that Gerard used a combination of the two dominant Arabic versions of the Almagest, one by Ḥajjāj and the other by Isḥāq ibn Ḥunayn and revised by Thābit ibn Qurrah, both of which he follows over large sections. A combined reception of the same two traditions has parallels in the Arabic, as can be seen, for example, in the manuscript London, British Library, Add. MS 7474; the manuscript contains Books I-VI of Ḥajjāj's version of the Almagest, which on several occasions has been supplemented in the margins by corresponding passages from Isḥāq/Thābit's alternative text.
The Latin translations of the Almagest, from Syria, Sicily and Spain, show that translations of scientific works tended to be made where written sources and living intermediaries of the 'new' sciences had become accessible to Western students. They further show that for a translation to be successful, external circumstances were as decisive as the quality of the translation itself. Although the Latin translators from Arabic kept close to the wording of their Arabic sources, each of them had to develop a suitable Latin terminology, and in that way facilitated an independent Latin treatment of astronomy. However, although the Almagest and various related works came to be widely studied in Latin Europe, it took until the fifteenth century for astronomical learning in Europe to develop from a passive reception of Ptolemy's doctrines to a critical and creative science.