This discussion has been interesting but far from complete on stories of ancient explorers reaching North or South America.   There are also accounts of Phoenicians and explorers from Carthage reaching these shores. Local, to Stone County, Arkansas, songster, Jimmy Driftwood wrote a song about Saint Brendan, an Irish monk crossing the ocean before 600 AD. Brendan wrote an account of that journey that described crystal palaces, mountains spouting fire, and monsters with catlike heads. A modern day explorer built a boat matching the description of the one used by Brendan and encountered icebergs, volcanoes, walruses, and whales. Columbus supposedly had a copy of Brendan's maps. Of course there are skeptics. A version of St. Brendan's Fair Isle can be found on Youtube.