This is a particularly interesting topic, since so many people object to the word, "discover" when applied to Columbus.
Yes, it is obvious that some Norse ships visited the New World, and probably even took word of it back to their country.
There is evidence to suggest that the Templars may have known of the New World, and may even have established a small base here.
Of course, there were already people here of various types, with some obviously having mixed far northeaster asian ties.
However, Columbus' journeys undeniably "discovered" the New World as far as the Old World was concerned. Only Columbus' voyage, along with the reports back to Europe, changed the whole flow of world history. If the Norsemen knew about the Americas, it apparently didn't have any real effect on their society, nor did they spread knowledge about it to other nations. But the whole social, economic, and religious structure of Europe was changed by Columbus' work, and eventually the whole world was changed as well.
By the same logic, nobody "discovered" Australia, Hawaii, or New Zealand. Nobody "discovered" Easter Island. After all, there is undeniable evidence that all had inhabitants at various times. However, they were "covered" by the ignorance of the whole world. Nobody, except for the people actually living there, knew that they existed. There was no commerce or communication with the rest of the world. So, the explorers who found them really did "discover" them, as they pulled back the cover of ignorance, presenting their existence to the rest of the world. Edited: Nighthawk on 17th Oct, 2004 - 2:24pm