No the ancient greeks thought that the earth was round. Think about it; they could see the shadow of the earth during eclipses and the shadow was round. They also noticed things like the horizon and ships slowly disappearing in the horizon.
And how quickly forget the statue of Atlas holding the earth on his back! So the idea that Columbus was gonna fall off the face of the earth was 1) a rumor that never died, or 2) those people were just incredibly stupid because people had known the earth was round for at least 1000 years.
I agree with Mafoo in that just because something is widely believed does not make it correct. Though Mr. Mafoo, even if 95% were in agreement, it wouldn't make then anymore correct. Logically speaking, that would be considered argumentum ad populum, or appealing to the masses. (i.e. 9 out of 10 doctors prefer toothpaste X!)
If 95% of the world thought the moon was made of cheese, it doesn't make it true ^_^. Likewise, 95% of the world believing in God does not prove nor disprove anything.
EDIT: http://en.wikipedia.org/wiki/Christopher_Columbus#Navigation_plans yeah it was a rumor that was popularized and the rumor never died out.
