Danny Mills, 21, made the find in a field near Sudbury in Suffolk.
The area was dotted with plush Roman villas and country estates in the second century.
The object, described as a rare example of Roman craftsmanship, has been donated to Ipswich Museum where it is now on display.
In the autumn of 2009, Mr Mills, a metal detector user, found a large bronze object whilst metal detecting in a field near Sudbury.
He immediately reported the discovery to Suffolk Archaeological Unit.