A pattern on the shard links the artifact to a region far from where it was found.
The fragment shows the left half of the Japanese character for "shu" (the Chinese pronunciation would be "zhou").
Humid conditions on the Japanese island where the mirror was found may have helped preserve the rare artifact.
Since the 1920s, pottery spanning thousands of years has turned up in Lake Biwaka. Archaeologist don't know why.
Using new imaging techniques, scientists find "invisible" message on back of a pottery shard.
Two "matching" towns from the Basketmaker period were discovered in neighboring sand dunes