To the west stretched what was known as the Sea of Darkness, about which even the cool knowledge of the geographers and astronomers could not think steadily. Nothing was known about it, it did not lead anywhere, there were no people there, there was no trade in that direction. The tides of history and of life avoided it; only now and then some terrified mariner, blown far out of his course, came back with tales of sea monsters and enchanted disappearing islands, and shores that receded, and coasts upon which no one could make a landfall. The farthest land known to the west was the Azores; beyond that stretched a vague and impossible ocean of terror and darkness, of which the Arabian writer Xerif al Edrisi, whose countrymen were the sea-kings of the Middle Ages, wrote as follows: “The ocean encircles the ultimate bounds of the inhabited earth, and all beyond it is unknown. No one has been able to verify anything concerning it, on account of its difficult and perilous navigation, its great obscurity, its profound depth, and frequent tempests; through fear of its mighty fishes and its haughty winds; yet there are many islands in it, some peopled, others uninhabited. There is no mariner who dares to enter into its deep waters; or if any have done so, they have merely kept along its coasts, fearful of departing from them. The waves of this ocean, although they roll as high as mountains, yet maintain themselves without breaking; for if they broke it would be impossible for a ship to plough them.”