Greek traders in Egypt prospered greatly under the peace imposed by the Roman Empire. Their commerce with Arabia, East Africa, and India grew to a wonderful development in the first century after Christ. About 77 A.D. was published by a Greek of Alexandria the celebrated “Periplus of the Red Sea,” a pilot’s manual not unlike the modern Admiralty “sailing directions.” This “Periplus” shows us that the Greeks by the middle of the first century knew the Zanzibar coast very well under the name of Azan or Azania. Among these Greek merchants trading with India was one Diogenes, who, on returning from a voyage to India in about 50 A.D., landed on the East African coast at Rhaptum (Pangani or the mouth of the river Rufu?). Thence, he said, he “travelled inland for a twenty-five days’ journey, and arrived in the vicinity of the two great lakes and the snowy range of mountains whence the Nile draws its twin sources.” As nothing is recorded about his return journey, it is more probable that he merely conversed on the coast with Arab settlers and traders who told him that at a distance of twenty-five days’ march in the interior began a series of great lakes from two of which were derived the twin sources of the White Nile; that farther to the south of the most western of these two lakes was a range of mountains of great altitude covered with snow and ice, and named for their brilliant appearance of white the Mountains of the Moon. The Nile, he was told, united its twin head-streams at a point to the north of these two great lakes, and then flowed through marshes until it joined the River of Abyssinia (the Blue Nile), and so reached the regions of the known. [Illustration: THE MOUNTAINS OF THE MOON: A GLIMPSE ON ONE OF RUWENZORI’S HIGHEST PEAKS.]