Found this on the History Channel's website.
Roman coins have been dug up in America, suggesting that perhaps the Vikings or Columbus weren't the first Europeans to visit the New World. The coins were found in locations as far afield as Texas, Venezuela and Maine. One stash was found buried in a mound in Round Rock, Texas. The mound is dated to approximately 800 A.D. In the town of Heavener, Okla., a bronze tetradrachm bearing the profile of Emperor Nero was found in 1976. The coin was originally struck in Antioch, Syria, in 63 A.D.