First through fourth centuries AD. Cast bronze made by the lost wax process in which a wax original is covered with molding material with a wax sprue (channel to receive molten metal) attached. The completed mold is heated to vaporize the wax and the metal is poured into the resultant void. In this instance, fragments of the mold material fell into the void and the ring was cast with deficiencies where those fragments lodged. Depending on the quality of the molding material (sand clay mix) that could have been a common problem. Defective castings would have been remelted with the metal and reused. This one evidently was lost in the process and rediscovered 2000 years later. Also of note is that the bit of the key is a block, uncut, because it must be matched to the lock mechanism. It would have been cut at the time that the lock was assembled. That bit of Ancient Roman Trivia is something we have never run across in our research! Intriguing and academic.