Islamize the Berber areas of the Sahara and the regions south of the desert. After winning over the Sanhaja Berber tribe, they quickly took control of the entire desert trade route, seizing Sijilmasa at the northern end in 1054, and Aoudaghost (Awdaghust) at the southern end in 1055. Yahya ibn Umar was killed in a battle in 1057, but Abdullah ibn Yasin, whose influence as a religious teacher was paramount, named his brother Abu Bakr ibn Umar as chief. Under him, the Almoravids soon began to spread their power beyond the desert, and conquered the tribes of the Atlas Mountains. In 1058 they crossed the High Atlas and conquered Aghmat, a prosperous commercial town near the foothills of the mountains, and made it their capital. They then came in contact with the Barghawata, a Berber tribal confederation, who followed an Islamic "heresy" preached by Salih ibn Tarif three centuries earlier. The Barghawata resisted. Abdullah ibn Yasin was killed in battle with them in 1059, in Krifla, a village near Rommani, Morocco. They were, however, completely conquered by Abu Bakr ibn Umar, and were forced to convert to orthodox Islam. Abu Bakr married a noble and wealthy Berber woman, Zaynab an-Nafzawiyyah, who would become very influential in the development of the dynasty. Zaynab was the daughter of a wealthy merchant from Houara, who was said to be from Kairouan. In 1061, Abu Bakr ibn Umar made a division of the power he had established, handing over the more-settled parts to his cousin Yusuf ibn Tashfin as viceroy, and also assigning to him his favourite wife Zaynab. Ibn Umar kept the task of suppressing the revolts that had broken out in the desert. When he returned to resume control, he found his cousin too powerful to be superseded. Abu Bakr ibn Umar founded the new capital of Marrakesh around this time. Historical sources cite a variety of dates for this event ranging from 1062, given by Ibn Abi Zar and Ibn Khaldun, to 1078 (470 AH), given by Muhammad al-Idrisi. The year 1070, given by Ibn Idhari, is more commonly cited by modern historians. Some writers cite the year 1062. In November 1087 Abu Bakr was killed in battle – according to oral tradition by an arrow – while fighting in the historic region of the Sudan. Yusuf ibn Tashfin had in the meantime brought the large area of what is now