I' ve voted greek, because it would be a total question for me, if PM would come only as Roman and Egyptian but not as a Greek.
Asian would make also a fine choice : Samurai, Shoguns, Ninja, all would be great for giant battlefields , for relaxation Geisha, even if you really want a monster in it as well: Godzilla, Modzilla, ...
And it would have also a link to the Spanish conquistadors, Marco Polo, Columbus (think boats,ships, silk, spices, buddha statues, ...)
Another theme could be The Italian Renaissance, the days of Assassin's Creed to speak, The doge, Milan, Venice (boats, gondoliers), Firenze ...
Seems they can go all the way as well with the Musketeers, the Louvre, ...