Legendary Islands of the Atlantic

We cannot tell at what early era the men of the eastern Mediterranean first ventured through the Strait of Gibraltar out on the open ocean, nor even when they first allowed their fancies free rein to follow the same path and picture islands in the great western mystery. Probably both events came about not long after these men developed enough proficiency in navigation to reach the western limit of the Mediterranean. We are equally in lack of positive knowledge as to what seafaring nation led the way.