Intro:
Its very difficult to design anything to feel ancient. Sure for buildings and tools and stuff you can use textures and make them look old and worn out, but that’s something different. I mean the aesthetics, the feeling, that something is traditional and its roots go far back in time. In some games you can achieve this by resorting to its own long history (vanilla/beta versions) e.g. if you play minecraft and only use oak planks and cobblestone it will look really oldschool.
Main part:
I think with African Royals the Developpers did something similar but way better. They had the problem of representing the rich and long history of Ethiopia (idk anything about Hausa), without letting them appear like primitive cavemen. They did an excellent job by referencing the look of Age of Empires 1 & 2 and combining it with Aoe3 graphics. Its really smart, not only because it credits its predecessors and thereby creates a sense of ‘age’, it also links the AgeofEmpires-timeline and connects the 3 games.
Here are some examples:
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Towers:
The upgrades are a direct homage to Aoe1 and when you select a tower, it also plays the same ‘shreeking’ sound -
Economy:
You can see the same picture for the Aoe1 and 3 gold upgrade.
but in terms of economy, the biggest connection is between Aoe2 and 3.
With the re-introduction of smaller fields arround the granary, it also refferences its upgrades. Notice how ethiopians lack “crop rotation” in Aoe 2 and they get it right at the beginning of Aoe 3!
3.Relics:
Sure, its just a small detail, but never the less…
artifacts and relics from Aoe 1 & 2.
Honourable mention: Berber Genitour… im sure i missed some other references too 
Hope you enjoyed this little digression! And let me know, if you found more 