All sea faring nations knew that the Earth wasn't flat. People even knew some time between 276 BC and 174 BC when Eratosthenes calculated the Earth's circumference (only off of the modern measurement by .8%) and he successfully calculated the Earth's axial tilt with nearly the same precision.

If European explorers had been up on their ancient Greek they would have known that there was more to the planet than Europe, Asia, and Africa.