If Renaissance voyagers had to overcome the fear instilled in them by the idea of the frigid and torrid zones before they could explore beyond the northern and southern limits of the inhabitable lands, they faced a different problem in dealing with the eastern and western ones. Here the boundaries of the oikoumene did indeed coincide with the limits of the land which came to an end in Ocean. In ancient Greece, Okeanos was a body of water thought to mark the edges of the world. Just as the idea of torrid and frigid zones had filtered from Greek thought into Roman, and from there into medieval geographies, so did the idea of Ocean. While the torrid and frigid zones provided climatic limits to the oikoumene in the ancient world, Ocean acted as a physical boundary which also posed a limit to human habitation.

This chapter examines the way in which Ocean was redefined in the fifteenth and sixteenth centuries so that it ceased to be seen as a confine and came to be considered the primary means of communication to connect different parts of the world to each other. It begins with an overview of the three different theories of Ocean which existed in the classical world. It then looks at how the understanding of Ocean was altered in a Christian Renaissance context. Despite the overarching emphasis on Ocean as a confine throughout classical and medieval times, there was much in the enduring idea of Ocean which could enable sixteenthcentury writers and travellers to reenvisage it as a means of communication. Far from limiting human inhabitation, Ocean provided the means for humans to have global interchange and exchange – the seas became the pathways of the oikoumene. The chapter then examines how, since Ocean surrounded all the different parts of the world, it was also thought to define the nature and extent of the landmasses. Because of their belief in the classical Ocean, humanists came to believe that the Americas must be a continent in their own right, entirely separated from Eurasia and Africa, by Ocean, but also connected with them for trade purposes by the same water that separated them. The chapter concludes by showing how the Christian and classical contexts worked together in the reenvisioning of the nature of ocean as a means of connecting all parts of the world.