You might want to research the Great Zimbabwe ruins. It was a stone city housing between 10,000 to 18,000 people, built between 1100 and 1500 and made entirely of stone blocks expertly positioned without mortar. It was the largest in Southern Africa but there were several other smaller stone cities from this era. They contained artifacts showing the people there traded with both China and Arabia. It was first seen by white men( Portuguese) in about 1530.
