Robert of Chester

fl. c. 1141-c. 1150

English Mathematician and Astronomer

Robert of Chester was one of the foremost medieval translators of Arabic scientific works into Latin. Through his translations he introduced Arabic algebra and alchemy to Western Europe. However, he is best known for making the first Latin translation of the Koran, the primary religious text of the Islamic religion.

Robert was born in the early twelfth century. As was common for scholars at the time, he was known to his contemporaries by many names, including Robert Retinensis, Robertus Ketenensis, de Ketene, Ostiensis, Astensis, Cataneus, and Robert Cestrensis. Chester apparently refers to where he was educated, as it is believed that he was originally from the town of Ketton in Rutland. Little else is known of his life. In 1136 he went to Barcelona to study with Plato of Tivoli (Plato Tibertinus), and by 1141 he was living near the Ebro studying alchemy and astrology with his close friend Hermann the Dalmatian (Hermannus Secundus). Robert was later Archdeacon of Pampelona in northern Spain (1143). He returned to England at least twice, once in 1147 and again in 1150. The date of Robert's death is not known.

In 1141 Peter the Venerable, Abbot of Cluny, found Robert and Herman engaged in their researches and convinced them to undertake the study of Islamic religion and law and to translate the Koran. Peter intended to use the fruits of their work in his diatribes against the "infidel" Muslims. Though Robert considered this a digression from his astronomical and mathematical researches, he completed the translation of the Koran by himself in 1143.

On February 11, 1144, Robert completed his translation of Jabir ibn Hayyan's (721?-815?) alchemical text Kitab al-Kimya. Retitled Liber de Compositione Alchemiae (The book of the composition of alchemy), it was the first Latin translation of an Arabic alchemical work to appear in Western Europe. The treatise recounts the story of the Umayyad prince Khalid ibn Yazid (died c. 704) who, according to legend, was the first Muslim to take a serious interest in alchemy. He supposedly studied with the Christian alchemist Morienus, who was a disciple of the well-known seventh-century Alexandrian alchemist Stephanos.

Robert introduced Western Europe to algebra with his Latin translation of Muhammad ibn Musa al-Khwarizmi's (800?-847?) al-Jabr wa'l-Muqabalah. Al-Khwarizmi's Algebra was the primary influence on the development of European algebra, determining its rhetorical form and much of its specialized vocabulary. The modern term algorithm is derived from the translation's first line, which begins "Dicit Algoritmi." The translation also contains the first use of sinus—from which the term "sine" is derived—in its modern trigonometric sense. Robert's translation appeared in 1145 (Gerard of Cremona [1114-1187] produced another translation in 1150). Because Abraham Bar Hiyya ha-Nasi's (fl. before 1136) Hibbur hameshihah we-ha-tishboret—the earliest exposition of algebra composed in Europe (written in Hebrew)—also appeared in 1145, this is generally considered the birth year of European algebra.

Robert also translated a number of astronomical works, including Ptolemy's (second century a.d.) De compositione astrolabii (On the composition of the astrolabe, 1147), al-Kindi's (801?-873?) De judiciis astrorum and al-Zarqali's (d. 1100) Canones. The latter work was one of several sets of astronomical tables Robert translated and updated. On a return trip to London in 1147, Robert made observations and read-justed these tables to the meridian of that city for the year 1150. He had previously made similar adjustments for Toledo based on the tables of Rabbi ben Ezra. Extracts from his various tables appear in De diuersitate annorum ex Roberto Cestrensi super tabulas toletnas. This volume also indicates that Robert had constructed a sexagesimal multiplication table containing all the products from 1 × 1 to 60 × 60.

STEPHEN D. NORTON