Pyramids

In 2300 BC, Nubia was first mentioned in Old Kingdom Egyptian accounts of trade missions. From Aswan, right above the First Cataract, southern limit of Egyptian control at the time, Egyptians imported gold, incense, ebony, ivory, and exotic animals from tropical Africa through Nubia. As trade between Egypt and Nubia increased so did wealth and stability."
More http://en.wikipedia.org/wiki/Nubia