[einhverfr]

One of the most interesting beliefs one runs into in the Middle Ages is the idea that although the world is round, it is impossible to travel across the equator by sea or land. This factors into medieval accounts of Alexander the Great for example.

[miguelpais]

Well, the portuguese navigators did have a lot of trouble crossing it. This was due to the fact that they mostly always sailed with the coast in sight, but when they reached the equator, there was just no winds or currents to keep pushing them, so they would just get stuck.

It took them a couple of years to find a way out of that point, by making huge turns westwards into the atlantic (which eventually led them to end up in Brazil, but that's another story...)

[DrStalker]

What did they think prevented this?

[einhverfr]

At least from the medieval literature I have read, it seems like there was a sense that divine retribution would prevent it. I.e. not necessarily about physical barriers but because it was hubris to attempt such a feat.