This is a bit of an oddity. While the four rings on the back for either a pair of straps or one continuous leather strap run through all four ( both methods work the same, the hand is passed through the strap/straps and when a fist is made the strap/straps are tightened giving sold control in the single hand ) are usually seen on Indo-Persian and Turk shields as is often the four front bosses each supporting one of the strap rings on the back side, the reinforcing straps and heavy rivets speaks to a more European manufacture. Perhaps one of the Eastern European states that was vasal to the Turks at various times and saw alot of mixing of military technology and tastes between east and west? Its quite possible that the missing item in the center is a parrying spike. I'm most used to seeing these on Highland targes of the 17th and 18th centuries but that doesn't mean the idea was new or strictly local to Scotland.
Its very simple, somewhat crude manufacture certainly lends itself to more of a munitions feel,a very stout serviceable piece with few frills. This is an Italian mid 16th century buckler we have for comparison
http://www.merctailor.com/originals.php?original_pk=105