In AD 789, Idris ibn Abdallah chose to create a new town on the right bank of the Fez River as the capital of his newly acquired empire. Many of the original residents were fleeing a rebellion in Cordoba (modern-day Spain). However, in 809, his son, Idris II, chose to establish his own capital on the opposite bank of the Fez River. Despite the fact that they were only separated by a short river, the cities evolved independently and remained two separate cities until they were merged in the 11th century by the Almoravids. This time, many refugees chose to settle in the new city, but this time they were fleeing an insurrection in Kairouan (in modern Tunisia). According to traditional traditions, one of these immigrants, Fatima al-Fihri, founded the University of Al-Karaouine (or al-Qarawiyyin) in 859. According to UNESCO and Guinness World Records, it is the world’s oldest continually operating university. On the other bank of the river, the Al-Andalusiyyin Mosque (or Mosque of the Andalusians) is also thought to have been founded by her sister in the same year.

Fez lost its title as a capital under the Almoravids, and it was relocated to the newly founded Marrakesh. Fez was a wealthy trading city during Almohad rule (12th-13th century), despite not being a capital. It even became the world’s largest city at the time, with around 200,000 people living there.