Exploration in ancient Egypt was fostered originally by the militaristic designs of the Pharaohs. Between the end of the Third Dynasty (c. 2600) and the Eighteenth (1570–1304), the Egyptian kings were continually extending their southern frontier, and bringing under their control the Ethiopians or Kushites of Nubia. The Sahara blocked any expansion westward, although it was certainly less extensive in those times and contained more abundance of water. The camel, however, had probably not been introduced into Egypt, and there was little incentive for traders to make long marches across the desert. Nigerian gold, ivory, and slaves were brought in by sea. Travel by boat up the Nile therefore remained the sole means of opening up new areas. Along with the military expeditions went scholars and explorers who brought back tales of the Upper Nile, which gradually came to the ears of Greek visitors to the Delta region in Mycenaean times. From the Homeric poems we may see in what form they were assimilated by the Greeks. At the edge of the river Ocean were said to dwell the Aithiopes, ‘burnt-faced men’, probably Somalis, while the story of the Pygmies who fought with cranes shows knowledge of the tribes of the interior. It is significant, too, that the name given to the Nile in Homer is Aigyptos, the river being equated with the country. There is however hardly any mention of Egypt in Greek literature between Homer and Hekataios. Not until 664 were Greeks encouraged to visit the country, and then Psammetik I brought in Lydian and Carian mercenaries perhaps by arrangement with the Lydian tyrant Gyges. By means of these troops he was able to break the power of the Kushites, who had established themselves as rulers over Egypt.