Baghdad was founded in 762 by the Abbasid caliph al-Mansur and became a great centre of learning. Under the caliphs, and notably al-Ma'mun (ruled 813-833), scholars gathered in what is known as the House of Wisdom (Bayt al-Hikma) to collect, translate and discuss books from Greek, Persian, Indian and Syriac sources. One of the leading translators was Hunayn ibn Ishaq (about 809-873), a Christian physician who led a team translating medical and philosophical works into Arabic and Syriac. This shows that the movement was a shared scholarly effort, paid for and protected by the state, in which scholars of different communities worked together. Translation was not a copy: scholars checked, corrected and extended what they received, and wrote new books. Historians still debate how organised the House of Wisdom was, and the picture of a single building should not be pressed too far, but the translation movement itself is well documented.