As the capital for his newly acquired empire, Idris ibn Abdallah chose to build a new town on the right bank of the Fez River in 789 CE. Many of the first inhabitants were refugees fleeing from an uprising in Cordoba (modern-day Spain). However, in 809 CE his son, Idris II, decided to found a capital of his own on the opposite bank of the Fez River. Even though they were only separated by a relatively small river the cities developed separately and became two individual cities until they were unified in the 11th century by the Almoravids. There were many refugees who decided to settle in the new city this time too, however this time they fled from an uprising in Kairouan (in modern Tunisia). The University of Al-Karaouine (or al-Qarawiyyin) is recorded by traditional sources as having been founded by one of these refugees, Fatima al-Fihri, in 859 CE. UNESCO and Guinness World Records consider it the oldest continuously-operating university in the world. The Al-Andalusiyyin Mosque (or Mosque of the Andalusians), on the opposite shore of the river, is likewise traditionally believed to have been founded by her sister in the same year.