They were a valuable culture because of their trading abilities. They were on the coast of the Red Sea. That gave them many ports from which they were able to trade. This culture, though, had many hardships. It declined in power many times, which forced it to break up into smaller kingdoms which flourished on their own. These are commonly referred to as the A-Group, B-Group, and C-Group. Their true decline was around 350 AD, when the kingdom of Axum invaded and broke up the culture once again. This time, the culture never recovered its strength, thus ending of Historic Nubia.
- "Journey to Ethiopia, Eastern Sudan, and Nigritia", an old book from the 1800s that talks about Nubia