Pedro Gallego

Page from a copy of Pedro Gallego's Summa de astronomia. The drawing depicts the relative positions of the planets on 1 May 1273.

Pedro González Pérez (c. 1197 – 19 November 1267), known as Pedro Gallego ( or Gallegus), was a Franciscan scholar and prelate. He was the first bishop of Cartagena from the diocese's restoration in 1248 until his death, and played a prominent role in organizing the church in the region of Murcia after 1243. He also compiled, abridged and adapted previous translations from Arabic into Latin, producing books on zoology, astronomy and economics.

Life Pedro was born about 1197 in Galicia, whence his nickname Gallego. According to the 18th-century historian Pablo Manuel Ortega, his birthplace was Santa Marta de Ortigueira and his father was Gonzalo Pérez Gallego. He was probably of noble birth, and may have been educated at the Franciscan convent of (Vallis Dei) near Santiago de Compostela, where he may have learned Arabic. He entered the Franciscan order before the Spanish peninsula was divided into separate provinces. According to Juan Gil de Zamora, he joined the convent of La Bastida in Toledo under the superior Alfonso Martínez shortly after its founding in 1219. The city of Cartagena submitted to Castilian rule in 1244 and Pope Innocent IV restored its bishopric,

In 1265, on account of the revolt of the Mudéjares, Pedro had to abandon the city of Cartagena and take refuge in the countryside, only returning after James I of Aragon had crushed the rebels and conquered Murcia. In 1943, Gaudenzio Melani discovered two chapters of a third work in the municipal library of Sarnano. Since then José Martínez Gázquez has discovered the rest of this work in a Spanish manuscript, now Biblioteca Nacional de España, MS 8918.

Although often labelled translations, Pedro's works are now seen as compilations and adaptations of existing translations. In the prologue to this work, Pedro says that he read Aristotle's Part of Animals in both Arabic and Latin, that is, the earlier translation of Michael Scot. For the first ten chapters, Pedro cites the work of Antecer and Abenfarag, probably the 11th-century Christian Arabic writers Ibn Zurʿa and Ibn al-Ṭayyib. It is for the eleventh and twelfth chapters that he cites Averroes (whom he calls Abuluatit Auenroyz). He also cites al-Fārābī (Abonacer). Juan Torres Fontes detected in De regitiva domus original ideas probably not found in his sources. Summa de astronomia (or Summa astronomica) is described in one incipit as "composed by friar Pedro Gallego ... all taken from al-Farghānī". According Marquant, the underlying work is the Liber de aggregationibus scientie stellarum, the work of al-Farghānī that existed in two Latin translations by Pedro's time, that of John of Seville and another by Gerard of Cremona. Pedro appears to have used the latter as his base text. According to Julio Samsó, the Summa is designed to demonstrate the sizes of and distances between various celestial bodies. It relies entirely on Latin sources, such as Martianus Capella and Macrobius, and Arabic sources translated into Latin by the school of Toledo, such as Averroes, al-Biṭrūjī and Ptolemy's originally Greek Almagest. These works were available in both Toledo and Galicia. Pedro's Summa exhibits a tendency to enlarge the universe, a tendency also found in other late medieval astronomers, such as Levi ben Gerson. For this reason, he relies more on Martianus and Macrobius, whose universe is larger, than on al-Farghānī and the Arabic tradition derived from Ptolemy.