Toledo fell to Castile in 1085 with its Arabic libraries and its Arabic speaking Christian and Jewish populations intact, and for a century and a half it was where Latin Europe went to get books. Gerard of Cremona came looking for Ptolemy's astronomy, stayed, learned Arabic and produced some seventy translations, including works of Aristotle, Euclid, Galen and Avicenna. The usual method needed two people: a Jewish or Mozarabic scholar read the Arabic aloud in Castilian, and a Latinist wrote it down in Latin, so the transmission was collaborative and interfaith by necessity. Alfonso X later had a comparable body of work produced in Castilian rather than Latin.
The consequences were enormous. The Aristotle that Paris and Oxford argued over for the next three centuries arrived by this route, together with the commentaries of Ibn Rushd and the philosophical theology of Ibn Sina and of Ibn Gabirol, whose Fountain of Life circulated in Latin without anyone realising its author was Jewish.
The city's two surviving synagogues show the other side of the story. Santa Maria la Blanca was built as a synagogue in Almohad style by Muslim craftsmen for a Jewish congregation under Christian rule, and El Transito was raised in the fourteenth century by the treasurer of Castile, with Hebrew and Arabic inscriptions across its walls. Both were taken over as churches, the first after the violence of 1391 and the second after the expulsion of 1492, and both stand today as museums of what the city stopped being.