The House of Wisdom (Arabic: بيت الحكمة; Bait al-Hikma) was a key institution in the Translation Movement - a library and translation institute in Abbassid-era Baghdad, Iraq. It is considered to have been a major intellectual center of the Islamic Golden Age. The House of Wisdom acted as a society founded by Abbasid caliphs Harun al-Rashid and his son al-Ma'mun who reigned from 813-833 CE. Based in Baghdad from the 9th to 13th centuries, many of the most learned Muslim scholars were part of this excellent research and educational institute. In the reign of al-Ma'mun, observatories were set up, and The House was an unrivalled centre for the study of humanities and for sciences, including mathematics, astronomy, medicine, chemistry, zoology and geography. Drawing on Persian, Indian and Greek texts—including those of Pythagoras, Plato, Aristotle, Hippocrates, Euclid, Plotinus, Galen, Sushruta, Charaka, Aryabhata and Brahmagupta—the scholars accumulated a great collection of knowledge in the world, and built on it through their own discoveries. Baghdad was known as the world's richest city and centre for intellectual development of the time, and had a population of over a million, the largest in its time. The great scholars of the House of Wisdom included Al-Khawarizmi, the "father" of algebra, which takes its name from his book Kitab al-Jabr.