Utah County's Deseret News web site reports that the Harold B. Lee Library (Brigham Young University) has on display "replicas of two 2nd-century, Roman, bronze metal plates that date back to A.D. 109". They are important, it seems, because they are "relevant to the Book of Mormon plates". BYU professor of law John W. Welch is quoted as saying that "This may be the best example of ancient writing on metal plates anywhere in the world".
Let me point out, firstly, that the university library also has the originals, and secondly, that they are examples of a very widespread phenomenon: the Roman auxiliary soldier's diploma, or guarantee of citizenship.
The BYU artefact is known to epigraphers (or students of inscriptions) as RMD III, 148. (It was published in 1993 by the late Margaret Roxan in her Roman Military Diplomas, volume 3: hence, "RMD III".) There, she noted that it had been issued on October 14, AD 109, to one Marcus Herennius Polymita, who had probably been recruited to his unit, cohors I Montanorum, in AD 84. The diploma was discovered in the Roman province of Moesia Superior, some 30km from the legionary base at Viminacium.
So what has all this got to do with the Book of Mormon?!