The way the Unsullied's fighting style is described leads me to believe that their principle function is to act as a kind of hoplite phalanx, massed in close ranks, forming a wall of spears and shields that is all but impenetrable to both cavalry and infantry and reasonably well protected by their shields from most types of skirmishers. What do you think the three spears, with which the Unsullied are known to have trained, actually are? I can't recall ol' Gurmy ever actually specifying. Just in case they are ever created as units for an emergent Targaryen invasion.
