Marrakesh is possibly the most important of Morocco’s four former imperial cities (cities that were built by Moroccan Berber empires). The region has been inhabited by Berber farmers since Neolithic times, but the actual city was founded in 1062 by Abu Bakr ibn Umar, chieftain and cousin of Almoravid king Yusuf ibn Tashfin. In the 12th century, the Almoravids built many madrasas(Koranic schools) and mosques in Marrakesh that bear Andalusian influences. The red walls of the city, built by Ali ibn Yusuf in 1122–1123, and various buildings constructed in red sandstone during this period, have given the city the nickname of the “Red City” or “Ochre City”. Marrakesh grew rapidly and established itself as a cultural, religious, and trading centre for the Maghreb and sub-Saharan Africa; Jemaa el-Fnaa is the busiest square in Africa.