The Kensington Runestone
1362 CE (claimed)
The Kensington Runestone is a slab of greywacke discovered in Minnesota in 1898, bearing a runic inscription that claims a party of Norse explorers visited the area in 1362 — 130 years before Columbus. If genuine, it would prove that Norse explorers penetrated deep into North America in the 14th century. The stone has been the subject of one of the longest-running authenticity debates in American archaeology.