No-one had ever wanted to travel across the great oceans.
Sailors had only small ships and they were easily battered by storm waves.
As a result, people travelled overland or hugged the coast in their ships.
Many sailors also believed that if you went too far from land, you would fall off the edge of the world.
The Mappa Mundi is a map made before Tudor times, and it shows that no one was interested in the oceans.
