I’ll grant it’s possible. But that’s a long way from Proven, or even Likely. And Godwin was imagining the transportation of an entire self-supporting colony of monks, which seems far removed from Brendan’s little curraugh.
A lot of things are possible but there is no conclusive evidence that Europeans made it to the North American mainland before Columbus got here. Maybe it happened, but investigation of so many sites just turns out the same way over and over again, investigation shows the site is more recent than was believed, or it was made by Native Americans, or it doesn’t exist at all. A confirmation of Celts or Norse landing somewhere on the mainland wouldn’t be enormously surprising because it’s not impossible, but such confirmation hasn’t happened yet.
Also, dating some of these artifacts is difficult to impossible. Europeans trampled all over the same areas that Native Americas lived in, moved and altered stone structures, and built them on top of old campsites. Old charcoal found in the ground may have been left by Native Americans long before a European built a stone cairn, or been left by Europeans near some stone structure built by locals much earlier. The evidence needed would be something like iron tools or runes that could actually be dated.
It’s worth pointing out that there IS ample evidence of Norse habitation at L’Anse Aux Meadows in Newfoundland. No one doubts it any more:
It’s arguably not on the “mainland”, since Newfoundland is a largish island, but that seems like a quibble.
Agree, although I don’t know how you could reliably date iron tools or runes. There have, in fact, been arguments about the dates of runes found in the New World.
In addition (although more questionable):
and:
Missed the edit window:
ETA:Wikihas some results of investigation showing the construction of America’s Stonehenge was quite old. It still can’t rule out some Europeans making their way across the Atlantic somehow to do the construction, but once again, there’s no evidence that was the case, and lacking such evidence the reasonable conclusion is that it was built by Native Americans.
Yeah, just lacking a better term I used mainland.
Italians came to Niles, Ill and built a leaning tower there before Columbus.
Before Columbus made it to Ohio you mean.
Sure – you’ve never heard of Columbus, Ohio?
They even have a replica of his ship there.
And, many experts say that L’Anse Aux Meadows is not Vinland, that it was a smaller settlement, thus there is a quite possibly a larger settlement somewhere south- possibly under water. 
I rate the Kensington Runestone as a “maybe”. There’s no classic marks of a hoax, like the Cardiff Giant, Piltdown man, etc. It was slammed as a obvious hoax by Archaeologists and Historians pre 1960 as pretty much they all derided any Pre-Colombian “discovery”. Now sure, there are linguistic and rune-stylistic issues, but note that no two experts agree on what the issue is, and they keep going back and forth. Honestly, from any writing sample this small, arguing stylistic or linguistic issues is pretty bogus, as who knows the background of the one guy who wrote it? I mean, (making an example up) today you could say that only Germans use the little cross on a 7, but I personally know two guys who write like that, and only one of them speaks German. Of course for six decades every Archaeologist and Historian knew it had to be a hoax.
It is amazing the 180 by Archaeologists and Historians around 1960 as before that, pretty much anything at all other than Columbus was laughed off as “bunkum” and pseudoscience. I am not saying the Kensington Runestone is legit, but it more a “maybe” than many will admit.
So, I have grave doubts of any Celtic “colony” or exploring expedition that made it to America and back (Brendan *may *be based on a real story but yes, it’s mostly allegory as Dr. Drake sez.). But Norman, Breton, Irish, and Basque fishermen may have discovered the Grand Banks before 1492, and it’s certainly not impossible for a fishing boat to have wintered in America, perhaps to dry their catch. In fact, it’s more likely than not. It was common by 1539. But no year-round “settlements” are likely.
Sure, I guess Aliens built these:
There are also some odd things like Dighton Rock, which is not a hoax, but is of unknown origin. Certainly there are some letters, and not recent. Perhaps the Cortereal expedition? Others could be Native.
Another stone structure that is presumably Native American is a 885’ stone wall at Fort Mountain State Park in Georgia.
The problem is that if you start assigning the construction of all of these ruins to some pre-Columbian European group, you’d soon realize that the Americas had to have an amazing number of Europeans running all over it for a very long time.
There is plenty of precedent for such an island in Celtic myth, one of the most notable being the island of Avalon in Arthurian lore. In various versions, Arthur is mortally wounded in battle and is taken to the beach, where his sister is waiting with a barge to take him to Avalon to be healed and eventually return someday.
The book isn’t directly about the subject at hand, but Charles Mann’s “1491” describes not just a few but many dozens of complex cultures throughout the Americas, some of which were extant when Europeans showed up, others of which had disappeared long before.
On topic, perhaps the recent locals didn’t put the stones there, but an older group did.
There are several groups of local Native Americans who beg to differ.
http://nolumbekaproject.blogspot.com/p/to-preserve-that-which-is-sacred-by.html
This may be better suited for starting a different thread, but I very recently flipped through this book at the library, and got a strong Velikovsky/von Daniken vibe from it.
Not quite. He starts with his feet solidly based on facts and the works of other historians, but then when he smarts off on his own extrapolations, he gets kinda carried away.
One of his main points is that there were a lot more Natives here before Columbus than we thought, which is true if by “than we thought” you are thinking rather old & dated history. He then takes the very highest possible estimates and extrapolations.
As other historians have noted about this trend- wiki "Historian David Henige has argued that many population figures are the result of arbitrary formulas selectively applied to numbers from unreliable historical sources. He believes this is a weakness unrecognized by several contributors to the field, and insists there is not sufficient evidence to produce population numbers that have any real meaning. He characterizes the modern trend of high estimates as “pseudo-scientific number-crunching.” Henige does not advocate a low population estimate, but argues that the scanty and unreliable nature of the evidence renders broad estimates inevitably suspect, saying “high counters” (as he calls them) have been particularly flagrant in their misuse of sources"
Well, if the worst thing about Mann’s book is that he over-enthusiastically endorses a high estimate for native population pre-contact, that’s not an irredeemable sin. The bulk of the book is reportage based on the work of actual historians and archaeologists.
Cc