Fez was founded under the Idrisid rule during the 8th-9th century. It consisted of two autonomous and competing settlements. The migration of 2000 Arab families in the early 9th century gave the nascent city its Arabic character. After the downfall of the Idrisid dynasty, several empires came and went until the 11th century when the Almoravid Sultan Yusuf ibn Tashfin united the two settlements and rebuilt the city, which became today's Fes el Bali quarter. Under the Almoravid rule, the city gained the reputation for the religious scholarship and the mercantile activity. Fez was expanded during the Almohad rule and became the largest city in the world during 1170-1180 with the estimated population of 200,000.