Abu Zayd Ahmed ibn Sahl Balkhi () was a Persian Muslim polymath: a geographer, mathematician, physician, psychologist and scientist. Born in 850 CE in Shamistiyan, in the province of Balkh, Greater Khorasan, he was a disciple of al-Kindi. He also founded the "Balkhī school" of terrestrial mapping in Baghdad. Al-Balkhi is believed to have been the first to diagnose that mental illness can have psychological and physiological causes and he was the first to typify four types of emotional disorders: 1) fear and anxiety, 2) anger and aggression, 3) sadness and depression, and 4) obsessions. Biography According to Abu Muhammad al-Hassan ibn al-Waziri, who was a student of the polymath, Abu Zayd al-Balkhi was a man whose face was covered in scars that he acquired following a bout with smallpox. In addition to this, he had a reserved and isolated character, leading scholars to have a lack of knowledge on his personal life. Approximately around the time of al-Kindi's death, he traveled to Baghdad, where he spent close to a decade studying several subjects including philosophy, astronomy, natural sciences, and the disciplines of the Quran. Shortly after this, he went back to Balkh. There, Ahmad ibn Sahl, the ruler of Balkh and its surroundings, appointed him as secretary or writer. In reality, he was offered both a writing and a ministerial position by the emperor. Al-Balkh, on the other hand, declined the latter and accepted the former. The king respected his decision and rewarded him handsomely. Sometime after this, he traveled to Baghdad again, before returning to Balkh for the last time and staying there up until his death. Works Of the many books ascribed to him in the al-Fihrist by Ibn al-Nadim, one can note The Excellency of Mathematics and his On Certitude in Astrology. His Figures of the Climates (Suwar al-aqalim) consisted chiefly of geographical maps. He also wrote the medical and psychological work, Masalih al-Abdan wa al-Anfus (Sustenance for Body and Soul). A modern scholar describes the bulk of his works as "more than 60 books and manuscripts, meticulously researching disciplines as varied in scope as geography, medicine, theology, politics, philosophy, poetry, literature, Arabic grammar, astrology, astronomy, mathematics, biography, ethics, sociology as well as others." Figures of the Regions His Figures of the Regions (Suwar al-aqalim) consisted chiefly of geographical maps. It led to him founding the "Balkhī school" of terrestrial mapping in Baghdad. The geographers of