66.那些没有亲眼看到实际交易的作者：P. F. de Moraes Farias, “Silent Trade: Myth and Historical Evidence.” History in Africa 1 (1974): 9-24.
67.关于无声交易的古老神话：Yāqūt, in Levtzion and Hopkins, ed., Corpus of Early Arabic Sources for West African History, 11.
68.气候变化：Sebastian Lüning et al., “Hydroclimate in Africa During the Medieval Climate Anomaly.” Palaeogeography, Palaeoclimatology, Palaeoecology 495 (2018): 309-322; George E. Brooks, “A Provisional Historical Schema for Western Africa Based on Seven Climate Periods (ca. 9000 B.C. to the 19th Century).” Cahiers d’études Africaines 101.2 (1986): 43-62.