[mmooss]

(potential spoilers:)

How could anyone figure out the provenance of that rectangular gold object with the four semispheres?

Gold has been widespread and doesn't narrow it down much. I wondered if its abstract-ish design might be modern, but then it didn't seem worthwhile to the Met and I decided it might just be practical (I was somewhat right about practicality). I guessed that the fastners on the back were were post-Middle Ages.