The fun thing about this is that Somalis were one of the few Africans that built towns and cities with stone. Unlike others who used "natural materials" which degraded into nothing if abandoned which is why there's few archeological sites across much of the lower half of the continent.
Even If you go deep into Somali galbeed you'll find centuries old ruins of medieval somali towns and cities. Imagine what could be uncovered through archeology.
And you also mentioned the Galla hordes forced many somali cities to start building walls, one of the most important walls was the Wall around Harar built by the nephew and successor of Ahmad gurey, Nur ibn Mujahid. He put up the walls around Harar and this kept the diverse population of the city inside and isolated from their ethnic kin. This melting pot of ethnicities, including Somali, mixed over the centuries to form a new ethnicity called Harari.
It is important to note that Harari didn't exist as an ethnicity during the time of Imam Ahmad. Many ethiopians claim he's harari stupidly. Even though he was born in Hubat to a Somali knight lol.
When the futuh mentions Harari it simply means people from the city, it doesn't describe any ethnicity. However it would most likely be Somali.
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