Answer:
Beginning with the top-most layer (most recent) is necessary so as not to disturb or destroy fragile remains and the only real method. One couldn't start at the bottom and work their way up!
Explanation:
The spread of Islam into the Maghreb is an example of Arab invasion of North Africa. The Arabs send Muslim army to Maghreb (modern morocco) to battle against Byzantines and allies, and finally conquer most of the North Africa were many Berbers (locals of Maghreb) join the Muslim army. After Arabs gain more power in the region, the Berbers are now ready to adopt and convert to Islam as well as the Arabic culture.
Maybe there were no cures, vaccines, or antibodies at the time. Medicine was never completely discovered for centuries to come, which is why the Black Plague occurred during the medieval/Middle Ages.
