When Alexander conquered Egypt, very little was known about the Red Sea, and nothing about that part of the ocean that joins that sea, and which washes the coast of Africa on one side and the coast of Arabia on the other ; it was believed even afterwards that it was impossible to round the Arabian peninsula. Those who had tried on either side had abandoned their attempts. They used to say : “How would it be possible to sail the coasts of Arabia to the south, since the army of Cambyse, which crossed it in the north, almost all perished, and that of Ptolemy, son of Lagus, sent help to Seleucus Nicator in Babylon, suffered unbelievable hardship, and owing to the heat could march only at night ? 
The Persians had no kind of navigation. When they conquered Egypt, they brought the same spirit that had been theirs at home, and the negligence was so extraordinary that the Greek kings found that not only were they ignorant of the navigations of the Tyrians, the Idumæans, and the Jews in the ocean, but even of those of the Red Sea. I think the destruction of the first Tyre by Nebuchadnezzar and that of several small nations and neighboring cities of the Red Sea caused the loss of the knowledge they had acquired.
Egypt, in the time of the Persians, did not extend to the Red Sea : it contained only that long, narrow edge of land which the Nile covers with its floods, and which is contained on each side by mountain chains.  Thus the Red Sea had to be discovered a second time, and the ocean a second time ; and that discovery belonged to the curiosity of the Greek kings.
They went up the Nile, they hunted elephants in the lands that lie between the Nile and the sea ; they discovered the banks of that sea by land. And as this discovery was made under the Greeks, their names are Greek, and the temples are dedicated to Greek divinities. 
The Greeks of Egypt were able to engage in a very extensive commerce : they were masters of the ports on the Red Sea ; Tyre, the rival of every trading nation, was no longer ; they were not hindered by the country’s ancient superstitions  : Egypt had become the center of the world.