When Abraham and Plato Met in Barcelona

Medieval Barcelona was a unique meeting spot of Eastern and Western culture. A place where Jews, Muslims and Christians could mix. It was in Barcelona that the "first Jewish scientist" and one of the great Christian translators of the day conceived an ambitious plan to bring the wisdom of the Islamic and ancient worlds to an awakening Europe

Shay Eshel
The solar system according to Abraham Bar Hiyya, "Tzurat Ha'Aretz VeTavnit Kadurei HaRekia" (The Form of the Earth and the Pattern of the Heavenly Spheres), 1494, the National Library of Israel

There is an ancient Chinese curse that says: “May you live in interesting times”. Abraham Bar Ḥiyya indeed lived in interesting times. Yet, he managed to turn that curse into a blessing.

In 1065, around the time of Abraham Bar Ḥiyya’s birth, most of the Iberian Peninsula (today’s Spain and Portugal) was an integral part of the Islamic world, and had been for centuries. During his lifetime, the peninsula’s northern Christian kingdoms began conquering large swaths of territory from the Muslims. The Crusades taking place at the same time in the Middle East further spurred the “Reconquista” – the Christian re-conquest of Iberian lands from the hands of the infidels. Armed with the power of religious fervor and the sword, they managed to conquer all the cities in the north and center of the Iberian Peninsula.

One would assume that in a period of religious wars, Jews would suffer persecution. Images of the Inquisition, expulsion, forced conversion and Jewish martyrs being forced to hide their Judaism come to mind.

However, during Abraham Bar Ḥiyya’s own lifetime, very little of this came to pass. The Christian kingdoms remained relatively tolerant towards the Jews. The Muslims on the other hand, now the losing side in the conflict and on the defensive, began persecuting Jews and legislating strict regulations against them in the territories they still controlled.

Abraham Bar Ḥiyya grew up in a still-tolerant Muslim world and pursued higher studies in Zaragoza, which was a flourishing cultural center. But like many Jews living in those turbulent times, he eventually had no choice but to bid farewell to the world of Muslim culture and science and relocate to one of the nearby Christian kingdoms.

Abraham chose Catalonia, settling in its capital, Barcelona. There he met many Jews who were unfamiliar with Arabic and the rich world of Islamic science that also preserved the wisdom of ancient Greece and Rome. He decided to undertake the task of making the realms of science, geography and astronomy accessible to Jews. He began composing scientific essays in Hebrew, in which he combined his own knowledge with translations of ancient and Islamic sources. Yesodei HaTvuna U-Migdal Ha’Emuna (“The Foundations of Understanding and the Tower of Faith”) was an encyclopedic scientific work that summarized all the accumulated knowledge from the ancient and Islamic worlds relating to mathematics, geometry, astronomy, optics and music. Unfortunately, only the introduction and the first few parts have come down to us.

Drawing of Barcelona in the Early Modern period (1563), by Anton van den Wyngaerde

In Ḥibbur HaMeshiḥa VehaTishboret (“Treatise on Measurement and Calculation”‘), which was intended as a reference book for land surveying and contained complex formulas of arithmetic and geometry, Abraham not only included a basic collection of sources for the novice, but, in a first for the European reader, also the complete solution to the quadratic equation. The many and varied books of Abraham Bar Ḥiyya rightly earned him the accolade – “the first Jewish scientist”.

The book Tzurat Ha’Aretz VeTavnit Kadurei HaRekia (“The Form of the Earth and the Pattern of the Heavenly Spheres”) presented for the first time in Hebrew the geographical sciences of both the Islamic and ancient worlds, including the earth’s relationship to other stars and to the moon and the sun. Abraham Bar Ḥiyya went on to write many more books, including works on the Hebrew calendar, astronomy (which included the first appearance of trigonometric functions in Hebrew), philosophy and Judaism.

Illustration of a solar eclipse, from Tzurat Ha’Aretz VeTavnit Kadurei HaRekia (“The Form of the Earth and the Pattern of the Heavenly Spheres”) by Abraham Bar Ḥiyya, Switzerland, 1546, the National Library of Israel

And now we come to the second hero of the story.

The name of Abraham Bar Ḥiyya eventually spread to the Christian world that was then taking its first steps in the field of science. An Italian mathematician and astronomer by the name of Plato of Tivoli heard about the wisdom of Abraham Bar Ḥiyya and wanted not only to learn the basics of Islamic science from him, but also to disseminate his knowledge to the Christian world. Their meeting in Barcelona led to a longstanding friendship and collaboration. It is likely that Plato of Tivoli came to the city especially for this purpose. The Italian moved to Barcelona and lived there for about twenty years, where he continued to learn from the Jewish sage. Together, these two men, a Jew and a Christian, conceived a particularly daring and ambitious plan.

Abraham Bar Ḥiyya knew Hebrew, Arabic and Catalan, the language spoken in Barcelona. Plato of Tivoli knew Italian, learned to speak Catalan, and was of course fluent in Latin – the language of science and of European literature of the Middle Ages. And so, the two scholars embarked on a collaboration to translate into Latin the scientific writings of the ancient and Islamic worlds. Abraham would translate and explain to Plato in colloquial Catalan what was written in the Arabic sources, and Plato would translate and write it down in Latin. Together they compiled precious texts that became seeds of scientific knowledge, soon to spread across Christian Europe.

The duo translated a famous work by Ptolemy of Alexandria into Latin – the Tetrabiblos (Τετράβιβλος) or Quadripartitum (90–168 CE), which deals with philosophy, astrology and the constellations. This translation was studied for hundreds of years – in the Middle Ages and the Renaissance – in universities all over Europe. The book’s positive reception allowed other works by Ptolemy to be accepted, thus indirectly contributing to further developments in the fields of science and medicine in Europe.

Imaginary portrait (1584) of the astronomer and geographer Ptolemy of Alexandria (90–168 CE), whose book Tetrabiblos, on philosophy and the constellations, was translated into Latin by Abraham Bar Ḥiyya and Plato of Tivoli

Plato and Abraham worked together on other translations from Arabic of mainly astronomical and astrological writings, including the work Kitab al-Mawalid (“The Book of Birth”) by the scholar Abu Ali al-Hayat (770–835), the works of al-Battani (858–929) and much more. It’s worth bearing in mind that astronomy and astrology, which at that time were inextricably intertwined, contained a great deal of geographical information, complex calculations of angles, volume and area, as well as rich and valuable mathematical information.

But Plato of Tivoli was not satisfied with just translating other sources. He also wanted to share Abraham’s own wisdom, which he had written down in Hebrew, with the Christian world. Relying on the Hebrew he had learned during the years of their joint work, Plato of Tivoli, apparently after his friend’s death, translated the Treatise on Measurement and Calculation into Latin, thus bringing to the Christian world the basics of geometry, trigonometry and the science of algebra. The chapters dealing with division, including the complete solution to the quadratic equation, which were studied by many European scholars, greatly influenced the development of mathematics in Europe. Liber Embadorum, the Latin translation of Treatise on Measurement and Calculation, was one of the direct sources of inspiration for Practica Geometriae, by the well-known mathematician Fibonacci (Leonardo of Pisa, 1170–1250).

Abraham and Plato, a Jew and a Christian living in a war-torn region in 12th-century Spain, sat together and distilled the best of the Jewish, Islamic and European-Christian worlds of knowledge. What might have been a curse became a blessing in the form of a meeting of cultures and scientific progress. Indeed, the Middle Ages may not have been so dark after all.

In the Edelstein Collection for the History and Philosophy of Science at the National Library of Israel, there are a number of books by Abraham Bar Ḥiyya, including the Treatise on Measurement and Calculation, The Form of the Earth and the Pattern of the Heavenly Spheres and the Quadripartitum, Plato of Tivoli’s and Abraham Bar Ḥiyya’s joint translation of Ptolemy’s book. 21st century readers of Hebrew are in for a thrill when they realize that they can open up and read books on science and geography that were written over nine hundred years ago by one of the wisest and most prolific Jews who ever lived.

For all of Abraham Bar Ḥiyya’s books in the Edelstein collection at the National Library of Israel, click here.


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