blockade the city by sea, while Ibn Tashfin's son Tamim led the siege by land. The city finally surrendered in August 1084. Ghana Empire and the southern wing According to Arab tradition, the Almoravids conquered the Ghana Empire sometime around 1076 CE. An example of this tradition is the record of historian Ibn Khaldun, who cited Shaykh Uthman, the faqih of Ghana, writing in 1394. According to this source, the Almoravids weakened Ghana and collected tribute from the Sudan, to the extent that the authority of the rulers of Ghana dwindled away, and they were subjugated and absorbed by the Sosso, a neighboring people of the Sudan. Traditions in Mali related that the Sosso attacked and took over Mali as well, and the ruler of the Sosso, Sumaouro Kanté, took over the land. However criticism from Conrad and Fisher (1982) argued that the notion of any Almoravid military conquest at its core is merely perpetuated folklore, derived from a misinterpretation or naive reliance on Arabic sources. According to Professor Timothy Insoll, the archaeology of ancient Ghana simply does not show the signs of rapid change and destruction that would be associated with any Almoravid-era military conquests. Dierke Lange agreed with the original military incursion theory but argues that this doesn't preclude Almoravid political agitation, claiming that the main factor of the demise of the Ghana Empire owed much to the latter. According to Lange, Almoravid religious influence was gradual, rather than the result of military action; there the Almoravids gained power by marrying among the nation's nobility. Lange attributes the decline of ancient Ghana to numerous unrelated factors, one of which is likely attributable to internal dynastic struggles instigated by Almoravid influence and Islamic pressures, but devoid of military conquest. This interpretation of events has been disputed by later scholars like Sheryl L. Burkhalter (1992), who argued that, whatever the nature of the "conquest" in the south of the Sahara, the influence and success of the Almoravid movement in securing west African gold and circulating it widely necessitated a high degree of political control. The traditional position says that the ensuing war with the Almoravids pushed Ghana over the edge, ending the kingdom's position as a commercial and military power by 1100. It collapsed into tribal groups and chieftaincies, some of which later assimilated into the Almoravids while others founded the Mali Empire. The Arab geographer Ibn Shihab al-Zuhri wrote