Antique Mini Coin Brooch wih Glass Lid Centerpiece Marked AA

This brooch has tiny coins around one larger one in the center. The top part of the coins have a lady's face although I am unsure who it is (I am not familiar with coins). The back of the coins depict a man with a three horse chariot. It appears they are going off to battle. The writing looks like Greek letters, but I can't be sure. The pin stem seems to be silver and is stamped "AA". The metal coins are not magnetic. The glass centerpiece on the back is interesting, and I recently found out that it opens when I slid a knife blade into the side and opened it ... So, my question is, what is this glass centerpiece for? What would someone store in this? Is there a specific name for this type of brooch? I have seen mourning jewelry where a lock of hair could be kept in the jewelry, but this brooch seems different. Does anyone know about the mark? Thanks for looking!