Strabo Geography 1.1.8

[8] Perception and experience alike inform us, that the earth we inhabit is an island: since wherever men have approached the termination of the land, the sea, which we designate ocean, has been met with: and reason assures us of the similarity of those places which our senses have not been permitted to survey. For in the east ¹ the land occupied by the Indians, and in the west by the Iberians and Maurusians, ² is wholly encompassed [by water], and so is the greater part on the south ³ and north. ⁴ And as to what remains as yet unexplored by us, because navigators, sailing from opposite points, have not hitherto fallen in with each other, it is not much, as any one may see who will compare the distances between those places with which we are already acquainted. Nor is it likely that the Atlantic Ocean is divided into two seas by narrow isthmuses so placed as to prevent circumnavigation: how much more probable that it is confluent and uninterrupted! Those who have returned from an attempt to circumnavigate the earth, do not say they have been prevented from continuing their voyage by any opposing continent, for the sea remained perfectly open, but through want of resolution, and the scarcity of provision. This theory too accords better with the ebb and flow of the ocean, for the phenomenon, both in the increase and diminution, is every where identical, or at all events has but little difference, as if produced by the agitation of one sea, and resulting from one cause.