During late antiquity, Aksum in Ethiopia was a prosperous realm complete with literature (burnt by later invaders, according to tradition), minted coins and imperial conquests overseas in Yemen. Lying on the Roman monsoon wind trade route from the Red Sea over to India, a lot of trade passed by Aksum and filled its coffers, and its kings spent a great deal of energy extracting luxury resources for export within his own borders. Here is a modern reconstruction of how the Dungur palace in the capital of Aksum (built during the 3rd to 5th centuries AD) would have looked like. At a distance, the blockiness of it all is more than a little reminiscent of ancient Mesopotamian architecture, although it differs once you get some closer detail:

The ruins of the palace itself: