Marrakesh is one of the great citadels of the Muslim world. The city was fortified by Tashfin’s son, Ali ibn Yusuf, who in 1122–1123 built the ramparts which remain to this day, completed further mosques and palaces, and developed an underground water system in the city known as the rhettara to irrigate his new garden. In 1125, the preacher Ibn Tumert settled in Tin Mal in the mountains to the south of Marrakesh. He preached against the Almoravids and influenced a revolt which succeeded in bringing about the fall of nearby Aghmat, but stopped short of bringing down Marrakesh following an unsuccessful siege in 1130. The Almohads, Masmouda tribesmen from the High Atlas mountains who practiced orthodox Islam, took the city in 1147 under leader Abd al-Mu’min.