Islamic learning

Under the Umayyads (661–750), Islamic scholarship focused on Qur'anic matters. But the ‘Abbasid dynasty which followed promoted Hellenistic and humanistic learning in accordance with the doctrines of the officially favoured Mu'tazili school of Islamic interpretation. This school was founded in Basra by Wasil ibn Ata (700–748) and held that the Qur'an is a creature of the God and that god desires only the best for man, views rejected by the Ash'ariyyah and Athariyyah ("Textualist") schools now considered orthodox Sunni Islam.

In 800, Baghdad was the largest city in the world—and the first to have a population of over 1 million.
Questiones:
How many were there Baghdad 800 years ago?