Roman Bronze Key, 1st - 3rd Century AD
Bronze, 50 x 26, 14 mm (LxHxW). Normally this would be called a key ring, and it may very well be one. But the design seems to preclude wearing, or at the very least it would be very uncomfortable to wear. Very nice and complicated and hefty bit end. Extremely rare type.
This type would occasionally come up at the old Hans Shulman auctions. For a similar key, but not quite as nice, see page 22 - the top key The Lure Of The Lock
. A museum quality key.