In my story, a casket containing the secret to Greek Fire (which historians to this day have not been able to duplicate) is stolen from a vault beneath Hagia Sophia. I came up with the idea that the casket was made double walled and had a lock so well made that it could not be picked or broken. This is so that the integrity of the secret can remain intact. The story is set in the late tenth century. SO can anyone with any knowledge of locks and of iron smithing in general and of this early period in particular, tell me if this is even a plausible explanation, or should I come up with a different scenario? Say, someone chucked it overboard by accident or something. LOL. I know that the secret of Greek fire was a closely guarded one by the Byzantine rulers to the extent that no one person had all the knowledge of all the steps necessary to create it, but was created somewhat assembly line style. It was like having the atom bomb. I would appreciate any insight into this matter.