It was 6,000 years ago when the first invasions came to disturb the peace of the plains' hunters-gatherers. Due to climatic changes in Northern Africa, Cushite and Nilotic pastoral tribes moved south searching for better pastures. Technically and militarily superior, Cushites and Nilotes easily seized the East African natives. Shortly after, around 500 B.C., the Bantus entered from the west.

Migratory flows and interactions between the different peoples who visited these Highlands gave birth to all the tribes in today's Kenya. Bantus, Cushites and Nilotes defined their languages and customs, which survive today. Conversely, nowadays it is scarcely feasible to find descendants of those hunters-gatherers who first inhabited the Kenyan Highlands.

The east of Africa was associated from old times with the sources of the White Nile. However, at the dawn of the christian era, the region was still unknown for the big northern empires, Egyptians, Greeks and Romans. For many centuries it remained terra incognita. Herodotus (484? B.C.-430/420? B.C.), the Greek historian who narrated the Greco-Persian wars, was a great traveller and sailed the Nile up to the first cataract in Elephantine (Aswan). The ancient Egyptians were familiar with the Nile probably up to Khartoum, in Sudan, and the Blue Nile to its source in Lake Tana, Ethiopia. But neither Herodotus nor the Egyptians showed excessive interest in the birthplace of the White Nile.

The first known explorer of East Africa was Diogenes, a Greco-Roman-Egyptian trader who in 110 A.D. endeavoured southward, disembarking in the port of Rhapta, possibly today's Pangani, in Tanzania. In his work "Periplus through the Eritraean Sea" he described the coast of Azania (Tanzania?), and even travelled inland to spot two great lakes and a snowy range of mountains where the sources of the Nile were supposed to be located. A geographer called Marinus from Tyrus (Tyre) gathered this information, which finally reached Ptolemy (85/90 A.D.-165/168 A.D.). In 150 A.D., the eminent Greek astronomer, geographer and mathematician drew a map in which he placed a range of mountains, which he named Lunae Montes, with snowy peaks that fed the two large lakes where the waters of the White Nile rose. This gave birth to the legend of the mountains where moonlight reflected as in a mirror, the Mountains of the Moon. Ptolemy's maps were lost, but were later re-drawn by the Renaissance scholars in the 15th century (1482) after the instructions detailed by the author in his work Geographike hyphegesis. These cartographic works would persist as the reference source until the great explorations of the 19th century.