The Simek book is quite interesting. Of course it wasn't just the sailors. By the 13th century, pretty much everyone knew the world was round as it was a common description in popular literature. Their ideas of antipodes were rather funny and something the church struggled against for some time until the discovery of the New World but an end to the question.... And until Vasco de Gama proved them wrong, they might not have believed you could sail across the equator.... but they knew it was round.
But the Simek work is interesting beyond that. It's largely on the basis of his work and the understanding that Europeans often knew more about Asia than Europe that it's fairly clear what a unicorn was: it's what you get when you describe an Asian rhino using a horse as a reference point. (Pliny's description of a monoceros is also frighteningly like a rhino, although some things are exaggerated.)
But the Simek work is interesting beyond that. It's largely on the basis of his work and the understanding that Europeans often knew more about Asia than Europe that it's fairly clear what a unicorn was: it's what you get when you describe an Asian rhino using a horse as a reference point. (Pliny's description of a monoceros is also frighteningly like a rhino, although some things are exaggerated.)