Detachable Porpax

[Giannis K. Hoplite]

Supposedly the Spartans had invented a detachable porpax,which they kept safe when they didn't use their shields,in fear that the helots who took care of their masters' weapons could use them in a possible revolt.
But have you ever seen such a porpax? For a long time I though this porpax was in the type of the vatican shield,which clearly has placements for the aditional leather or felt lining.This is also clear in many sculptures and porpaxes with the thinner(later) metal band.In the two sides of this metal band there are curvatures of the metal which supported the detachable lining.
However,re-enactors have proven that the shield can be used without the lining,so not a very successful invention,right?
Now look in the interior of Philip's ceremonial shield.

I see the porpax missing,but I also see something like a cuirass' hinges,with the nail passed through them. I haven't got a better image,if anyone has... Any ideas? The most strange is that in the new museum in Vergina,the shield(and some other stuff) are desplayed differently,and the same porpax is seemingly restored there!

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Giannis