After its beginning in the 8th century, Islamic geography was patronized by the Abbasid caliphs of Baghdad. Various Islamic scholars contributed to its development, and the most notable include Al-Khwarizmi, Abu Zayd al-Balkhi (founder of the 'Balkhi school'), Al-Biruni and Avicenna. Muslim geography reached its apex with Muhammad al-Idrisi in the 12th century. Later developments took place under Turks, particularly under the Ottoman Empire, with notable scholars such as Mahmud al-Kashgari and Piri Reis.