The missing 9th legion

This morning I stumbled across this object in a bog, sticking out of the mud. Is it perhaps the remains of a Roman bronze ceremonial helmet? 
In AD 84, the battle of Mons Graupius took place near to here, on the slopes of Bennachie. A large force of 17,000 Roman soldiers led by Agricola took on 30,000 natives under the leadership of Calagacus.
According to the only contemporary account of the battle, Tacitus' The Life of Gnaeus Julius Agricola, the Romans emerged totally victorious, slaying some 10,000 of their opponents with the loss of only 360 on their own side.
One of the Roman units fighting on that day was the ninth legion, the IX Hispana. The 9th was to become infamous when, in around 108 AD, 5000 battle-hardened men simply disappeared from the face of the Earth whilst on campaign, somewhere in Northern Britain. Perhaps I have found evidence of the disappearance .....? Certainly the helmet has seen some action, note the deep sword cut in the edge of the crest.