The disc, being flat, has no real horizon. Any adventurous sailor who got funny ideas from staring at eggs and oranges for too long and set out for the antipodes soon learned that the reason why distant ships sometimes looked as though they were disappearing over the edge of the world was that they were disappearing over the edge of the world.

The Light Fantastic: (Discworld Novel 2) (ed. Random House, 2009) - ISBN: 9781407034393