Its geographical position was favorable to this twofold object. For, on one side, the valley of the Nile, singularly fertile, must have early occasioned a numerous population; and, on the other, the Red Sea, giving communication with Arabia and India, and the Nile with Abyssinia and the Mediterranean, Thebes was thus naturally allied to the richest countries on the globe; an alliance that procured it an activity so much the greater, as Lower Egypt, at first a swamp, was nearly, if not totally, uninhabited. But when at length this country had been drained by the canals and dikes which Sesostris constructed, population was introduced there, and wars arose which proved fatal to the power of Thebes. Commerce then took another route, and descended to the point of the Red Sea, to the canals of Sesostris (see Strabo), and wealth and activity were transferred to Memphis. This is manifestly what Diodorus means when he tells us (lib. i. sect. 2), that as soon as Memphis was established and made a wholesome and delicious abode, kings abandoned Thebes to fix themselves there. Thus Thebes continued to decline, and Memphis to flourish, till the time of Alexander, who, building Alexandria on the border of the sea, caused Memphis to fall in its turn; so that prosperity and power seem to have descended historically step by step along the Nile; whence it results, both physically and historically, that the existence of Thebes was prior to that of the other cities. The testimony of writers is very positive in this respect. "The Thebans," says Diodorus, "consider themselves as the most ancient people of the earth, and assert, that with them originated philosophy and the science of the stars. Their situation, it is true, is infinitely favorable to astronomical observation, and they have a more accurate division of time into mouths and years than other nations" etc.