Upvote:1
The Archimedes Heat Ray seems to be a good example.
Upvote:13
I'll start with the archetypical story of the type: Troy.
Up till 19th century, people believed that Homer's and Virgil's troy was a legend, not a real city (unlike Greeks and Romans).
In 1865/1868, Calvert and especially Heinrich Schliemann have found what they believed to be real Troy (though later archaeology, fully detailed on Wikipedia, showed that Schliemann actually found earlier Troy II, whereas Homeric Troy is usually though not conclusively placed as Troy VIIa).
Upvote:17
I think the Norse discovery of the Americas fit. Around year 1000, an expedition led by Norseman Leiv Eiriksson winter camped on Newfoundland.
From the Wikipedia article:
For some centuries after Christopher Columbus' voyages opened the Americas to large-scale colonization by Europeans, it was unclear whether these stories [of Leiv Eiriksson's discovery of Vinland, my remark] represented real voyages by the Norse to North America. The sagas were first taken seriously when in 1837 the Danish antiquarian Carl Christian Rafn pointed out the possibility for a Norse settlement in or voyages to North America. North America, by the name Winland, was first mentioned in written sources in a work by Adam of Bremen from approximately 1075. It was not until the 13th and 14th centuries that the most important works about North America and the early Norse activities there, namely the Sagas of Icelanders, were put into writing.
The question was definitively settled in the 1960s when a Norse settlement was excavated at L'Anse aux Meadows in Newfoundland by archaeologist Anne Stine Ingstad and her husband, outdoorsman and author Helge Ingstad.
Icelanders (and Norwegians from the 1800s onwards) might have been "certain" all along that the stories of discovery were true, but I do not think it was accepted by everyone in the rest of Europe / North America until the archeological discoveries. There are several other, unconfirmed stories of trans-Atlantic contact, so it would have been feasible to group the Nors*m*n with these as long as no "hard evidence" was found.