Lower Egypt, the fertile Black Lands, and Upper Egypt, the arid Red Lands, were united when the ruler of Upper Egypt, King Menes, conquered Lower Egypt, founding the 1st Dynasty around 3100 B.C.

“The living Heru; Who prospers the Two Lands; the Two Ladies: Who prospers the Two Lands; the Golden Heru: Who prospers the Two Lands; King of Upper and Lower Chem: Neferkare; the Son of Re: Sha[baka], beloved of Ptah-South-of-his-Wall, who lives like Re forever.” 

–- From the Shabaka Stone