Madoc ap Owain Gwynedd
When Thomas Jefferson sent Lewis and Clarke across the continent, he told them to watch out for blue-eyed, Welsh-speaking Indians. Why?
In the mid-twelfth century or so, Owain Gwynedd had been at war, trying to maintain Welsh independence from the English and their king, Henry II. After Owain's death in 1170, his seventeen sons (and possibly two daughters) fought over who should be the next ruler of Gwynedd--Dafydd and Rhodri killed their elder half-brother, Hywel, and for the next 20 years Gwynedd was divided between them and their brothers.
Supposedly, one brother refused to participate. Madoc ap Owain--who is not listed in the genealogies as Owain's son, but may have been illegitimate (provided he was real)--set sail, leaving Wales for a land of peace. He went west, and came to a land that he thought was uninhabited; he returned to Wales, gathered a group of followers, and set sail, never seen again. Reports surfaced during the 1500s that Madoc had found North America; reportedly, there are pre-1492 documents that claim a Madoc found a country to the west, returned, and left again with settlers.
If so, it is assumed he landed in Mobile Bay, Alabama. Why? There are pre-Columbian stone structures--forts--which are unlike any known structures made by the Cherokee, who have legends that "white people" built them. Reportedly, these forts are uncannily similar in structure to Dolwyddelan Castle in Gwynedd, Madoc's home in Wales. The forts stretch northward into Tennessee; the Cherokee legend says that the whites were forced to move north, towards what is now Missouri, and that they intermarried with the people there.
Eighteenth and nineteenth century explorers reported coming across tribes of beareded, blue-eyed Indians who spoke a language similar to Welsh; the tribe was the Mandan people (now extinct, thanks to our government's wonderful policies of genocide... wait, wrong node for that).
Not everyone believes this theory. Though some scholars point to the similarities between the language of these tribes and of Welsh, others dismiss it as coincidence. Some point to the forts (which archaeologists do say are pre-Columbian), and others say it is another coincidence. Others point to the fact that the only accounts of Welsh-speaking blue-eyed beareded Indians comes from eye-witnesses--people who claimed to have met them. (Well, I don't know what they're looking for as proof if they won't accept that--not when there are several accounts, the majority by non-Welsh explorers. They'd have to throw out all of history, or a belief in anything they haven't seen with their own eyes, which leaves very little. But that's just me.)
Some, like Geoffrey Ashe, prefer to think St. Brendan the Navigator got here in the sixth century; others prefer to think it was Leif Erikson (no denying that one, really); and some still cling to the idea that Christopher Columbus is the real discoverer of America; others claim Egyptians, Phoenicians, Atlanteans, Hebrews, Chinese, aliens... Personally, I think it was the Neolithic tribes of pre-history; everyone else is simply an invader.
Was Madoc real? Probably. Did he sail to another land? Sure, why not? Was that land North America? Couldn't tell you. But it makes a neat story.